Citation
Fourth progress report

Material Information

Title:
Fourth progress report
Series Title:
Progress report - Tidal inlet management at Jupiter Inlet
Alternate Title:
UFL/COEL (University of Florida. Coastal and Oceanographic Engineering Laboratory) ; 91/008
Creator:
Mehta
Place of Publication:
Gainesville
Publisher:
Coastal and Oceanographic Engineering Department, Univeristy of Florida
Publication Date:
Language:
English

Subjects

Subjects / Keywords:
Jupiter Inlet (Fla) ( LCSH )
Tidal inlets -- Florida
Genre:
serial ( sobekcm )
Spatial Coverage:
North America -- United States of America -- Florida -- Jupiter Inlet

Notes

Funding:
This publication is being made available as part of the report series written by the faculty, staff, and students of the Coastal and Oceanographic Program of the Department of Civil and Coastal Engineering.

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All rights reserved, Board of Trustees of the University of Florida

Full Text
UFL/COEL-91/008

TIDAL INLET MANAGEMENT AT JUPITER INLET: FOURTH PROGRESS REPORT
by
A. J. Mehta T. M. Parchure C. L. Montague R. J. Thieke E. J. Hayter

and R.B.

Krone

June 1991
Sponsor:
Jupiter Inlet District 400 North Delaware Boulevard Jupiter, FL 33458




REPORT DOCUMENTATION PAGE
1. Report no. 2. 3. RecipLent's Accession No.
4. Title and Subtitle 5. Report Date
TIDAL INLET MANAGEMENT AT JUPITER INLET: June 1991
FOURTH PROGRESS REPORT 6.
7. Athor(s) A. J. Mehta R. J. Thieke a. Performing Organization Report No.
T. M. Parchure E. J. Hayter and UFL/COEL-91/008
C. L. Montague R. B. Krone
9. Performing Organization Name and Address 10. ?roject/Task/Work Unit o.
Coastal and Oceanographic Engineering Department
University of Florida 11. Contract or Grant No.
336 Weil Hall C 89 -002
Gainesville, FL 32611 13. Type of Report
12. Sponsoring Organization Name and Addreas
Jupiter Inlet District Commission Fourth Progress Report
400 North Delaware Boulevard
Jupiter, FL 33458
14.
15. Supplementary Notes
16. Abstract
In this progress report on the Jupiter Inlet Management Study we have made
observations and tentative conclusions with regard to the protocol for sand
bypassing at the inlet, the problem of sand movement around the south jetty, influx
of sediment in the interior region of the Loxahatchee River estuary, sedimentation
in the area of marina docking facilities, mining of the ebb shoal, offshore rocky
outcrops, mangroves and seagrasses.
17. Originator's Key words 18. Availability Statement
Hydrodynamics Jupiter Inlet
Littoral drift
Loxahatchee River
Salinity intrusion
19. U. S. Security Classif. of the Report 20. U. S. Security Classif. of This Page 21. No. of Pages 22. Price
Unclassified Unclassified 238




UFL/COEL-91/008

TIDAL INLET MANAGEMENT AT JUPITER INLET:
FOURTH PROGRESS REPORT
by
A. J. Mehta
T. M. Parchure C. L. Montague
R. J. Thieke E. J. Hayter and

R. B. Krone
Sponsor:
Jupiter Inlet District
400 North Delaware Boulevard
Jupiter, FL 33458

June 1991




TABLE OF CONTENTS

PAGE

LIST OF FIGURES . . . . . . . . . ....
i
LIST OF TABLES .......................
I. SYNOPSIS . . . . . . . . . .
1.1 Introduction ........... .......
1.2 Some Observations and Tentative Recommendations .

II. SAND TRANSPORT NEAR INLET MOUTH .........
2.1 Introduction. . . .........
2.2 Physical Model Experiments: Drogue Studies 2.3 Long-Term Longshore Transport Simulations

.5
10
13
13 13
20 20 20 27

III. INLET NEARFIELD ..........
3.1 Introduction ..........
3.2 Waves in the Study Area
3.3 Offshore Channel ....
3.4 Ebb Shoal Volumes ....
3.5 Mining of Ebb Shoal . .
IV. INLET INTERIOR MODELING ...
4.1 Introduction. .........
4.2 Model Application ....
4.3 Model Results ......
V. STORM SURGE LEVELS ......
5.1 Introduction ........
5.2 Martin County Data ...
5.3 Palm Beach County Data .
5.4 Conclusion ...............
VI. SAND TRANSFER CONSIDERATIONS
6.1 Introduction . . ...
6.2 Site Conditions . ...
6.3 Proposed Development . .
6.4 Littoral Drift . .
6.4.1 Previous Estimates

6.4.2
6.4.3

~~~~
o

Dredging Data Analysis .. .. University of Florida Study . .
6.4.3.1 General........
6.4.3.2 Estimated'Annual Drift .
6.4.3.3 Estimated Monthly Drift 6.4.3.4 Estimated Daily Drift .

6.4.4 Characteristics of Littoral Drift at
Jupiter . . . . . . . .
6.5 Sediment Budget .. .. .. .. .. .. .. .
6.5.1 General . . . . . . .
6.5.2 Primary Distribution" n. .un.i..
6.5.3 Secondary Distribution and Return Flows




6.5.4 Total Distribution. ...... .. .. 94
6.5.5 Sources of Southward Sand Transfer .. .94
6.6 History of Beach Nourishment at Jupiter.......95 6.7 Comments on Beach Erosion .............99
6.8 Options for Sand Transfer Systems..........101
6.8.1 General .... 101
!6.8.2 Promising Alternatives...........102
6.8.3 Second-Best Alternatives . . .... 106
;6.8.4 Discarded Alternatives..... .. . 108
6.9 Design Parameters for Sand Transfer System ... 111
6.9.1 Interception Mode/Storage Mode .. .. ..111 6.9.2 Sand Trap Location and Size ..........113
6.9.3 Rate of Sand Transfer. .......... 113
6.9.4 Sand Transfer Season............114
6.9.5 Estimation of Pump Capacity ..........116
6.9.6 Design of Fluidization System .. ......117
6.10 Cost Estimates . . . . . .. .. .. ...117
6.10.1 Other Projects .... ...... .....117
6.10.2 Cost Estimate for Jupiter Inlet . . 118
6.11lConclusions . .. .. .. .. ... ... ...124
6.12 General Recommendations..............124
6.13 A Possible Sand Transfer System for Jupiter
Inlet.......................125
VII NAVIGATIONAL ISSUES ...................155
VIII ENVIRONMENTAL CONCLUSIONS. ...............159
8.1 Sea Turtle Nesting. ................159
8.2 Offshore Rocky Outcropping .............160
8 .3 Mangroves .. .. .. .. .. ... .. ..... 161
8.4 Seagrasses and Seagrass Mitigation ..........161
IX REFERENCES.........................172
9.1 For All Chapters Except Chapter 5...........172
9.2 Reference for Chapter 5........ ........178
APPEND ICESi
A Review of Selected Sand Bypassing Systems in
operation .o. ........o... ...o..o... ...180
A.1 Selection Parameters. ..... ............180
A.2 Information on Existing Systems.o...........180
B Details of Conventional Sand Transfer Systems. ......187
B .1 General . . .. .......o.. ... ...187
B.2 iFixed Bypassing Plants........ . .. .. ..187
B.2.1 South Lake Worth Inlet, Florida.. .....187 B.2.2 Lake Worth Inlet, Florida..........188
B.2.3 Rudee Inlet, Virginal Beach, Virginia oo189
B.3 Floating Bypassing Plants..............191
B.3.1 Port Hueneme, California o...... o. 191
B.3.2 Channel Islands Harbor, California . .o191 B.3.3 Jupiter Inlet, Florida........ .........192
3




B.3.4 Sebastian Inlet, Florida ........... 192
B.3.5 Santa Barbara, California ... ......... .193
B.3.6 Hillsboro Inlet, Florida ... ............ 194
B.3.7 Masonboro Inlet, North Carolina ...... 194
B.3.8 Perdido Pass, Alabama . ......... 195
C New Technology for Sand Transfer System ......... 197
C.1 General ........ .................... 197
C.2 Split Hull Barges . . ............. 198
C.3 Submarine Sand Shifter ..... .............. .199
C.4 Jet Pump .......... ................... .199
C.5 Fluidization ........ .................. 201
D Corrigendum to First Progress Report: Part II
(UFL/COEL-90/005) ........... . . . . . 207
E Data from the Offshore Wave Gage . . ........ 230




LIST OF FIGURES

FIGURE PAGE
2.1 Approximate inlet and shoreline configuration and
model template lines for physical model drogue
studies . . . ..................... 30
2.2 20-year longshore transport simulation with annual
dredging of 45,000 cubic yards showing volume of
nourished sand on south beach with no critical
shoreline recession ....... .................. ..31
2.3 20-year longshore transport simulation with annual
dredging of 45,000 cubic yards showing volume of
nourished sand on south beach with substantial
shoreline recession beyond critical levels ...... 32
2.4 20-year longshore transport simulation with annual
dredging of 45,000 cubic yards showing volume of nourished sand on south beach with near-critical
shoreline recession due to a single large
transport year ........ .................... 33
i
3.1 Proposed alternative offshore channel alignments
and sand borrow area, and wave measurement stations
in the physical and mathematical models ........ .49
3.2 Numerically simulated ebb flow pattern near Jupiter
Inlet; reference wave height is 1.21 ft, period 4 sec,
direction NE and inlet velocity 3.61 fps (1.1 m/sec) 50
3.3 Numerically simulated flood flow pattern near Jupiter
Inlet under same conditions as in Fig. 3.2 ...... 51
3.4 Offshore wave energy over a 19 year period in the
Jupiter Inlet area, and ebb shoal volumes ........ ..52
i
3.5 Capital dredging volume required as a function of
design eastern channel cross section at Jupiter Inlet
using 1986 bathymetry ...... ................. ..53
i
3.6 Schematic of ebb shoal and area of mining ......... ..54
4.1 Finite element grid of the Loxahatchee River estuary 58
4.2 Predicted tides at Jupiter Inlet for March 1-30,
1991, used for ocean boundary conditions ....... ..59
5.1 Location map ........ ..................... 70
5.2 Combined total storm tide frequencies for Martin
County (Ref: 5) ........................... 71




5.3 Estimated frequency of storm surge levels for
Martin County (Ref: 6) .................. 72
5.4 Hurricane tracks passing through Palm Beach County,
Florida, and vicinity during the period 1871-1970 . 73
i
5.5 Storm surge frequency curve for Palm Beach County
(Ref: 7). ......... 74
6.1 Sand trap located within Jupiter Inlet .. ........ ..127
6.2 Proposed developments at Jupiter Inlet .. ........ ..128
i
6.3 Present locations of dredging in Intracoastal
Waterway and locations of disposal areas .. ....... ..129
6.4 Estimated percentages of quantities of southward and
northward alongshore sediment transport ... ........ ..130
6.5 Log-normal probability plot of annual longshore
transport magnitudes (southward and northward) from
WIS hindcasts for the period 1956-1975 . . . . 131
6.6 Estimated percentages of duration of occurrence of
southward and northward alongshore sediment transport 132
6.7 Monthly net quantities of littoral drift estimated
for the year 1967 ........ ................... .133
6.8 Percentage of net littoral drift each month, estimated
from 20 years WIS wave data ..... .............. .134
6.9 Cumulative net southward longshore transport at
Jupiter Inlet calculated from WIS hindcast data for
the year 1967 (increasing volume implies net
southward transport) ...... ................. .135
6.10 Primary littoral drift distribution at Jupiter Inlet 136
6.11 Secondary littoral drift distribution at Jupiter
Inlet ..........................137
6.12 Return flows of littoral drift distribution at Jupiter
Inlet . . . ....................... 138
6.13 Quantities of total distribution of littoral drift
At Jupiter Inlet ....................... 139
1
6.14 PernttaLe of total distribution of littoral drift
at Jupiter Inlet ....... ................... .140
6.15 Offshore borrow areas for beach nourishment projects
at Jupiter (Aubrey and DeKimpe, 1988) ... ......... ..141




6.16 Location of nourishment areas in the four projects
at Jupiter Island, 1973-1987 (Aubrey and DeKimpe,
1988) . . . . . . . . . 142
6.17 Profile lines and instrument location map (Shemdin
et al., 1976) ........... . . . . . . 143
6.18 Types of littoral barriers for which sand transfer
systems have been used (U.S. Army Engineers, 1984) . 144
6.19 Modified beach restoration plan proposed in 1983
(Arthur V. Strock & Associates, Inc., 1983) ...... 145
6.20 The present feeder-beach plan and the proposed
dredging options (Coastal Planning and Engineering,
1989)1 ..................................... 146
6.21 Plan of improvements proposed at Jupiter Inlet by
U.S. Army Engineers District, Jacksonville, FL in
1966 (Gee and Jenson, 1963) .... .............. 147
6.22 Jetty weir proposal of 1969 ..... .............. .148
i
6.23 Financing projections for the proposed Jupiter
Inlet jetties ......... ..................... .149
6.24 Yearly quantity of sand transferred south of Jupiter
Inlet ............................. 150
6.25 Four-year moving averages of sand transferred to
south beach and estimated annual deficit on the
south beach ........................ 151
6.26 Flow chart on the selection of sand transfer system
at Jupiter . ........................ 152
6.27 Schematic layout of recommended sand transfer system 153
6.28 Recommended areas for disposal of dredged material . 154
8.1 Good seaturtle nesting beach near the Hilton Inn at
Jupiter, Florida, looking north toward Jupiter Inlet 164
8.2 Beach-slope profile south of Jupiter Inlet near
the Hilton hotel at Jupiter, Florida on three
occasions in 1990 1991 . . . . ......165
8.3 Steep scarp discouraging to nesting seaturtles just
south of the south jetty at Jupiter Inlet, Florida,
looking south toward the Hilton hotel ... ......... .166




8.4 Beach-slope profile just south of the south jetty
at Jupiter Inlet, Florida on three occasions in
1990 1991 . . . . . . . . . .
8.5 Location of rocky outcroppings in the vicinity of
Jupiter Inlet, Florida (adapted from Continental
Shelf Associates, 1985; 1987; 1989b; 1989c) ....
8.6 Drawing of Jupiter Inlet, Florida from Captain
Miller, showing location of bottom rocks just
inside the inlet . . . . . . ....
8.7 Location, canopy height, and number of mangroves
in mangrove forests in the Loxahatchee River
estuary east of the railroad bridge ............
8.8 Location, density, and total weight of seagrasses
in seagrass beds in the Loxahatchee River estuary
east of the railroad bridge..... .............
C.1 Sand pump construction and operation (Clausner,
1988) . .........................
C.2 Steps involved in fluidizing technique and examples
of layout of fluidizing pipes (DYNEQS Ltd., 1990;
Parks, 1989) . . . . . . . . . .
C.3 Schematic functioning of fluidizer and sand pump
(DYNEQS Ltd., 1990; Parks, 1989) .........

D.1 Comparison of changes in sea bed contours outside
Jupiter Inlet: March 1979, August 1979 and
February 1980 .....................
E.1 Jupiter wave data for November, 1990: (a) Modal
period, T ; (b) Significant wave height, H1/3;
(c) Wave direction; (d) Wave spreading parameters
S and P2; (e) Current velocity, Uc; (f) Current
direction, Oc; and (g) Tide .... ............
E.2 Jupiter wave data for December, 1990: (a) Modal
period, Ts; (b) Significant wave height, H1/3;
(c) Wave direction; (d) Wave spreading parameters
S and S2; (e) Current velocity, Uc; (f) Current
direction, ; and (g) Tide ... ............
E.3 Jupiter wave data for January, 1991: (a) Modal
period, T ; (b) Significant wave height, H1/3;
(c) Wave Eirection; (d) Wave spreading parameters
S, and .2; (e) Current velocity, Uc; (f) Current
direction, Oc; and (g) Tide .............

. 229

. . 231 . 233 . 235

167
* 168
169
* 170
171
* 204
205 206




E.3 Jupiter wave data for February, 1991: (a) Modal
period, T ; (b) Significant wave height, H1/3;
(c) Wave direction; (d) Wave spreading parameters
SI and S2; (e) Current velocity, UC; (f) Current
direction, 8c; and (g) Tide . . ............ 237




LIST OF TABLES

TABLE PAGE
2.1 Final positions (given in terms of physical model
template numbers) of spherical floats two minutes after placement along south beach during maximum
flood tide under the following prototype conditions:
Reference wave height = 4 feet, Wave period= 8 seconds, Reference wave angle = 31 degrees
from north, Water elevation: MSL, Beach level:
Normal ............. .. ... ... .....22
2.2 Final positions (given in terms of physical model
template numbers) of spherical floats two minutes after placement along south beach during maximum
flood tide under the following prototype conditions:
Reference wave height = 4 feet, Wave period =
8 seconds, Reference wave angle = 31 degrees from
north, Water elevation: MSL, Beach level: Nourished ..23
2.3 Final positions (given in terms of physical model
template numbers) of spherical floats two minutes after placement along south beach during maximum
flood tide under the following prototype conditions:
Reference wave height = 8 feet, Wave period =
12 seconds, Reference wave angle = 31 degrees from
north, Water elevation: +8.0 feet, Beach level:
Normal..........................24
2.4 Final positions (given in terms of physical model
template numbers) of spherical floats two minutes after placement along south beach during maximum
flood tide under the following prototype conditions:
Reference wave height = 8 feet, Wave period =
12 seconds, Reference wave angle = 31 degrees from
north, Water elevation: +8.0 feet, Beach level:
Nourished.........................25
3.1 Wave heights at Stations S2, S3 and S6 obtained by
mathematical model simulations .............35
3.2 comparison of wave heights (from NE) at Station S2
between mathematical and physical model simulations ..36
3.3 Estimated capital dredging volumes in the proposed
channel alternatives as functions of bathymetry . . 37
3.4 Ebb shoal volumes at Jupiter Inlet ...........38
3.5 Wave heights at several stations obtained by
mathematical model simulations under existing and
modified conditions' .a 45




3.6 Wave heights at several stations obtained by
mathematical model simulations using different
bathymetric surveys. . . . . . . . . 45
4.1 Sediment fluxes in Jupiter Inlet channel . . . 57
5.1 Combined total storm tidal values for various
return periods, Martin County, Florida (Ref: 5) . . 62
5.2 Frequency of storm surge levels for Martin County,
Florida (Ref: 6) . . . . . . .......63
5.3 Hurricanes affecting Palm Beach County, Florida,
1871-1970 (Ref: 7) ....................... 64
i
5.4 Frequency of storm surge levels for Palm Beach
County, Florida (Ref: 7) ..... .............. 68
5.5 Estimated return period for storm surge levels for
north Palm Beach County ...... ................ 69
6.1 Estimates of annual littoral drift at Jupiter Inlet 78
6.2 J.I.D. and Army Corps dredging records for
Jupiter Inlet (Dixon and Associates, Personal
Communication, 1991) ........................ .80
6.3 History of Jupiter Inlet and Intracoastal Waterway
dredging and placement of disposal material on the
shoreline south of Jupiter Inlet (Continental Shelf
Associates, Inc., 1989a) ............. . . 81
6.4 Estimated longshore transport values (Q cubic yards
per year) for 20 year period 1956-1975 (calculated
from WIS wave hindcast data) .... ............. 83
6.5 Estimated percentage of duration of occurrence of
southward and northward drift for 20 year period
1956-1975 (calculated from WIS wave hindcast data) . 84
6.6 Estimated net monthly littoral drift for the year
1967 .......... ......................... 85
6.7 Estimated monthly magnitudes of littoral drift,
based on 20 years (1956-1975) WIS wave data ...... 87
1
6.8 Estimated monthly magnitudes of net southward and
northward littoral drift based on 20 years
(1956-1975) WIS wave data ..... ............... ..88
6.9 Beach nourishment projects at Jupiter Island,
Florida (Aubrey and DeKimpe, 1988) . . . 0 . 96

I




6.10 History of shoreline maintenance/construction at
Jupiter Island, Florida (Aubrey and DeKimpe, 1988)

. 98

6.11 Grainisize comparisons at Jupiter island, Florida
(Aubrey and DeKimpe, 1988) . . . . . . . 98
6.12 Economic analyses of bypassing options at Indian
River Inlet (U.S. Army Engineers, 1989) ........ 119
6.13 Prices on bypassing at various locations, 1989
level (Bruun, International Marine Science and
Engineering, 1991) ....... .................. 120
6.14 Annual cost comparison of alternative bypassing
systems for Sebastian Inlet (Coastal Technology
Corporation, 1988) .... . 122
6.15 Cost comparison for various alternatives. DYNEQS
"CHAN/NAV System" (Fluidized Sand Bypassing).
("Typical Inlet" costs create and maintain for
20 years) .......... .......................123
A.1 Depressed weir/jetty and trap .... .......... . 182
A.2 Trap in entrance/channel dredging ............ 183
A.3 Detached breakwater and trap ..... ............. .184
A.4 Transfer from shoals . .............. 184
A.5 Fixed/movable plants ...... ................. ..185




I. SYNOPSIS

1.1 Introduction
This fourth progress report on the management study of Jupiter Inlet covers the period 2/5/91 through 5/31/91. Findings reported here must b e reviewed in conjunction with the first three progress
reports (Mehta et al., 1990a, 1990b and 1991a) Note that since the study is continuing, additional findings will be reported in the
fifth and final progress report. In what follows, some observations and tentative recommendations are summarized; details are given in the body of the report, as well as previous progress reports.
1.2 Some Observations and Tentative Recommendations
1. A two decade period for the management plan as envisaged for
this study is reasonable, provided a commensurate plan f or growth management is considered concurrently. Furthermore, if the rate of sea level rise increases by a factor of 10 over the next two or three decades as predicted by some studies,
management priorities will have to be adjusted on a continual basis. Since, however, it is unclear if an increased rate of rise has already begun, no immediate response or studies to
determine what response should be taken are recommended.
2. Sand transfer from the JID trap on a more frequent basis than
in the past, e.g. at least once a year, is recommended to provide a more stable feeder beach. on the average, the annual amount of sand to be pumped from the JID trap plus the Corps
of Engineers dredging should be around 60,000 yd3 as opposed to around 43,000 yd3 in the past years. This would be a desirable option for minimizing the problem of sand dispersal from the south beach. We recommend a slightly larger JID trap
to make it more efficient for catching incoming sand.
3. continuous or near continuous transfer, e.g. with the use of
a dedicated sand pump installed in the trap, is a technically feasible and perhaps economical option which may benefit sea
turtles as well.




4. Annual, pumping of sand f rom the trap prior to the non-pumping
window (June 1 October 30) will afford greater summer sand supply to the south beach and tend to reduce the extent of
maximum shoreline recession.
5. Coordination of JID trap dredging with dredging by the Corps
of Engineers is recommended in view of items 2 and 4. This will allow sufficient sand to be available to optimize the
sand transfer operation.
6. A measurable fraction of the south beach sand, particularly
the pumped sand, reenters the inlet under summer and winter
waves, and thereby reduces the efficiency of the sand transfer operation. Therefore, any beach renourishment project south of the inlet must address this "leakage" problem, since returned sand merely adds to the cost of sand transfer. Leakage here
means sand moving around the jetty, not through it.
7. 'The bleach area immediately south of the south jetty is
inherently subject to strong wave attack during storm waves modified by the south jetty. It is recommended that the option of discharging sand at a point that is just (about 1/3 mile)
south of the area of critical erosion be considered. While this option would "sacrifice" a short segment of the public beach immediately south of the south jetty, it would provide
sand to that part of the beach which is inherently more stable, this in turn would mean better retention of the pumped sand. 'Furthermore, during the summer months in particular, the unnourished beach segment immediately south of the south jetty will receive sand from the feeder beach due to the net
northward transport.
8. The wider part of the Loxahatchee River west of the Florida
East Coast Railroad bridge continues to accumulate sandy and
organic sediment at a rather slow rate. This is a natural estuarine process which typically occurs where sea and river waters mix under tides and waves. The three sources of this sediment are: 1) river arms and the Intracoastal Waterway, 2)
the Ocean, and 3) local bank erosion.




9. A possible means to reduce the inf lux of sand from east to
west past the railroad bridge ( 1, 000 to 3, 000 yd3 depending upon the grain size) is the dredging of a relatively small new trap immediately westward of the railroad bridge in order to
catch the incoming sediment.
10. A measurable contributor to local bank erosion and
redistribution of sediment inside the inlet area is believed
to be boat-wake- induced water motion. Boat speeds must be
regulated in the interior channels.
11. Marina docking facilities along the south bank of the inlet,
east of the U.S. 1 bridge, are natural recipients of sediment
as they are located along the inner bend of the river. Sand is believed to accumulate there at the rate of about 16 cm /year.
Two marinas located westward of the bridge are enclosed basins with single entrances, better protected from sedimentation. It is impractical to enclose the docks east of the bridge by protective structures, because such structures could materially alter the tidal, salt water and turbidity regimes of the river. Reducing the influx of sand in the area of the marina docking facilities by a more efficient sand trapping
and pumping operation in the inlet would be the means by which the sedimentation problem could be alleviated. The abandoned
basin near Dubois Park does have a potential as a viable marina from the point of view of available water depth, provided sedimentation in it is controlled by narrowing its entrance by protective structures, adequate flushing of the
waters is ensured, and a maintenance dredging program is
instituted.
12. The ebb shoal is an integral component of the inlet system,
the sand having been accumulated there by the presence of the
inlet: itself. At Jupiter Inlet, a small fraction (around 14, 000 yd) of the littoral sand is believed to be "lost"
annually to the interior waters and/or the offshore; hence, in the absence of other sources of sand, the ebb shoal is a resource for the Inlet District that can be used to replenish
"lost" sand to the south beach over a long term basis. We

I I




offer the possibility that the ebb shoal be dredged for that purpos ;e, taking out around 150, 000 yd3 every ten years. Any larger or more frequent mining operation must be avoided unless post-dredging monitoring of the hole created by the removal of 150,000 yd3 indicates permissibility of increasing the mining operation in terms of the amount to be mined and
the frequency of mining. The 150, 000 yd3 of sand should not be removed (in the manner of a dredged navigation channel) from the landward portion of the ebb shoal since that would interfere with the flow of sand bypassing the inlet, and may enhance nearby beach erosion. Suitability of sand for
placement on the south beach should be verified while
selecting the area of the ebb shoal for dredging.
13. Sincelthe net annual littoral sand drift along the coast is
southward, transferring sand to the south beach has different meaning than f or example transferring sand to the north beach.
When a significant quantity of sand is transferred from the
ebb shoal to the south beach, that sand is "lost" from the inlet'system in the sense that refilling of the ebb shoal by natural processes can be slow. Sand placed on the beach north
of the inlet from the ebb shoal is likely to return to the ebb
shoal at a measurably greater rate.
14. Sea Turtle Nesting: Nesting sea turtles require 1) access to
a nesting site, 2) "'diggable" sand, and 3) a stable beach for
incubating eggs.
Although many variables affect the selection of a nest
site by a turtle, one which is most relevant to beach nourishment is beach-profile slope. Profiles of beaches that
are used by turtles near Jupiter Inlet have a slope of roughly 1 foot of rise per 10 to 20 feet of run in the zone from mean sea level to about 100 feet toward land. Beaches with steep scarps in this zone are unlikely to be chosen by turtles for
nesting.
Sand coming from traps and the ebb shoal is of a grain
size suitable for nest excavation by turtles. It is similar to the sand now on the beach in areas frequently used by turtles.




Finer perhaps such as that found in the flood shoals west of the railroad bridge, may become too compact for
turtles to excavate.
The heavily eroded beach immediately south of the south
jetty is problematical. Restoration of the beach is desirable, yet the presence of the south jetty causes this area to have
a comparatively high erosion potential. Hence, added sand can suddenly disappear during a storm. The restored beach becomes an "attractive nuisance" to nesting turtles. Eggs laid in this stretch of restored beach are at a much greater risk of being
washed out before hatching than eggs laid on a more stable beach. To solve this problem, all nests must be relocated, turtles must be prevented from nesting in this area (perhaps with a fence) or a certain amount of nest loss must be
tolerated.
continuous sand pumping, as opposed to intermittent
dredging, is a desirable option with respect to sea turtle nesting and general beach ecology. Unlike intermittent
dredging, continuous pumping does not cause sudden alteration of beach profiles and burial of existing organisms. Sudden perturbation of the beach requires a period of ecological
recovery and may discourage nesting turtles.
15. Offshore Rocky Outcroppings: Although rocky outcroppings
appear and disappear throughout the bare-sand area surrounding the inlet, the only major group of presently exposed
outcroppings that lies within the probable impact area of inlet management operations is that at Carlin Park. Like all
rocky: outcroppings these are habitat for nearshore fishes.
Those'at Carlin Park are shallow, very near shore, and hence also have recreational value to snorkelers. Natural sand
transport may occasionally bury these outcroppings (and reexpose others) in the absence of any human activity.
Nevertheless, it is recommended that beach nourishment
activities avoid burying these rocky outcroppings.
16. Mangroves: About one-half of the mangroves in the area east of
the railroad bridge are in the intertidal zone of the Dubois 17




Park lagoon. The Dubois Park lagoon is also very close to the inlet. Another 40% are in the south arm of the intracoastal waterway (the portion considered part of the study region
ended at Burt Reynolds Park).
Mangroves occupy the intertidal zone, the extent of which
is determined by the slope of intertidal lands and the range of the tides. Changes in mean water level, tidal range, or sediment loading can change the extent of area occupied by mangroves. Changes in inlet management that could create these effects are not recommended. Options of potential impact include changes in inlet cross-sectional area or in the crosssectional area of the "bottle-neck" to flow at the railroad
bridge.
Perhaps the main area of concern should be the tiny inlet
of the Dubois Park lagoon. Alterations in this small inlet may change the intertidal and subtidal parts of the lagoon. Such alterations are not recommended and do not seem necessary to
achieve inlet management objectives.
17. Seagrasses: Almost half of the seagrasses in the study region
east of the railroad bridge are found in one bed along the south shore just opposite the entrance to the north arm of the intracoastal waterway. Another smaller but densely populated bed is just west of that one, on the eastern edge of the marina area. Other less dense beds occur in Dubois Park lagoon, in the north arm of the Intracoastal Waterway and along most of the edges of the estuary west of the north arm of the Intracoastal Waterway. Seagrass density decreases in the more western beds (immediately west of the U.S. 1 bridge and in the south arm of the Intracoastal Waterway). North of the S.1R. 707 bridge to Jupiter Island, seagrasses are denser
than found elsewhere within the study region.
Seagrass bed success is dependent on many factors, but
good light penetration, moderate tidal range, stable sediments, low fluctuation in salinity, and gentle bed slope are very important. Seagrasses east of the railroad bridge occur in shallow water where light can penetrate sufficiently

II I




and where frequent exposure to air, scour, or high temperature do not occur. Where bed slopes are gentle, the suitable area for growth is large. Changes in water level, tidal range, turbidity, and fluctuation in salinity will influence seagrass beds. These types of change are not expected unless management options affect the cross-sectional area at either the inlet, the "bottle-neck" at the railroad bridge, or the tiny inlet of the Dubois Park lagoon.
Perhaps the greatest threat to seagrass beds, however, is changing bathymetry, especially by dredging, but also perhaps by the movement of flood-tidal shoals. Broad, shallow zones that support seagrasses are unsuitable for navigation and marinas. These zones must either be avoided by boats, or else the loss of seagrasses must be tolerated. Although seagrasses can stabilize shoals, the shoals must first be stable enough to allow the initial growth of the grasses. Existing seagrass beds may be buried by rapid shoaling or eroded by altered flow patterns. Any inlet modification that buries, destabilizes, or erodes existing seagrass beds should be avoided, or damaged beds should be appropriately mitigated.




II. SAND TRANSPORT NEAR THE INLET MOUTH

2.1 Introduction
The progress in the study of the sediment transport patterns in the exterior portion of Jupiter Inlet and the resulting. evolution of the south beach is presented in two parts. The first part reviews the results of a series of physical model drogue experimentsidesigned as a follow-up to the sequence of field sand tracer experiments described in prior reports (Mehta et al., 1990b, Mehta et al., 1991a). The second part describes the continuing application of the statistical model of longshore sand transport to produce long-term simulations of erosion patterns on the south beach under various sand bypassing scenarios.
2.2 Physical Model Experiments: Drogue Studies
In an effort to gain additional understanding about the sediment pathways around the immediate exterior of Jupiter Inlet, two sand tracer field experiments were conducted during June 1990 (typical summer conditions), and an additional experiment run in December 1990 (winter conditions). The detailed results of these experiments are presented in Mehta et al., (1990b) and Mehta et al., (1991a), but the general conclusions are as follows:
a. South beach sand moves into the inlet on the flood tide during periods of wave activity from the southeast and from
the northeast as well.
b. The time scale of this sediment movement is relatively short, since most of the observed motion occurred generally in
under two tidal cycles.
c.' Large quantities of sand appear to move into the inlet
relatively close to the south jetty.
d. Some sediments remain in the system for long time
periods.
The apparently large-scale motion of south beach sand into the inlet !during flood tide, particularly under northeast wave




incidence, has raised the question of whether or not a "dividing line" exists along the south beach, south of which sand will not move into the inlet. A series of physical model tests- were
designed and implemented to test this possibility as well as to provide a standard against which to evaluate possible design modifications to the existing south jetty.
To trace the flow patterns south of the inlet, model tests were conducted in the 1:100 scale physical model of Jupiter Inlet located at the Coastal and Oceanographic Engineering Laboratory at the University of Florida (previously described in Mehta et al., 1991a). Flow visualization was achieved through the use of small floating plastic balls which could be followed readily by eye and
by photographic techniques. The model "grid" for tracking the floats-is shown in Fig. 2.1. The model templates are spaced evenly at 1 foot distances approximately along the shoreline of the model
south beach '(note the distance between templates corresponds to 100 feet along the prototype beach) Template number 29 corresponds to the location of the south jetty, with the template numbers decreasing in a southward direction.
All experiments were performed by placing small colored
plastic balls in shallow water at various template locations along the south beach and monitoring their positions for a two minute time period. At the end of the two minutes the final position of the float was recorded (in terms of a model template number). If
the float entered the inlet during the experiment, the time at which it pa ;ssed the "time line" indicated on Fig. 2.1 was recorded instead. ten floats were placed at each location for each test condition chosen. The results are shown f or a variety of test conditions in Tables 2.1-2.4.
In each case the experiments were run for maximum flood tidal current with a wave direction of 31 degrees from north. The
shoreline corresponded either to normal or nourished conditions along the south beach, and the reference wave height in prototype units was either 4 feet, with a period of a seconds (normal conditions), or 8 feet, with a period of 12 seconds (storm conditions), which gave a total of four experimental runs. The




Reference wave height = 4 feet
Wave period = 8 seconds
Reference wave angle = 31 degrees from north
Water elevation: MSL
Beach level: Normal
Note: An asterisk (*) before an entry denotes that float passed into the inlet during the experiment, in
which case the elapsed time of travel is noted.
Initial Float Position (Model template #)
Float 29.0 28.0 27.5 27.0 26.5 26.0 25.0
1 0:46 1:30 0:55 0:51 0:59 26.5 4.5
2 0:18 1:00 0:49 0:56 25.5 27.0 8.0
3 0:25 0:46 1:55 1:28 1:26 24.0 5.5
4 0:26 0:51 0:46 1:19 1:10 6.5 6.5
5 0:15 1:24 1:14 1:01 2:32 5.5 8.0
6 0:23 1:04 0:57 0:53 26.5 26.5 5.5
7 0:20 0:55 0:34 1:06 0:53 9.0 7.5
8 0:19 0:50 0:45 1:03 26.5 25.5
9 0:16 0:46 0:35 0:48 26.5 20.0
10 0:17 0:41 *.0:31 0:49 1:05 25.5

I

Final positions (given in terms of physical model template numbers) of spherical floats two minutes after placement along south beach during maximum flood tide under the following prototype conditions:

Table 2. 1: 11




Reference wave height = 4 feet
i Wave period = 8 seconds
Reference wave angle = 31 degrees from north
Water elevation: MSL Beach level: Nourished
Note: An asterisk (*) bef ore an entry denotes that float passed into the inlet during the experiment, in
which case the elapsed time of travel is noted.
Initial Float Position (Model template
Float 29.0 28.0 27.5 27.0 26.5 26.0 25.0
1 0:50 0:33 0:25 0:33 0:32 0:39 18.0
2 0:33 0:32 28.0 0:26 0:39 0:41 9.0
3 29.0 0:35 0:28 0:29 0:41 28.0 13.0
4 28.5 0:29 0:27 0:28 0:30 1:12 25.0
5 0:38 1:44 0:26 0:27 0:35 0:55 22.0
6 29.0 0:26 0:23 0:36 0:40 1:15 1:43
7 2:12 0:58 0:23 0:26 0:54 28.0 14.0
8 0:27 0:26 0:44 0:22 0:37 1:48 17.0
9 0:28 0:20 0:29 0:23 0:32 1:00 28.0
10 29.0 0:26 0:56 0:26 0:41 28.0 7.0

Final positions (given in terms of physical model template numbers) of spherical floats two minutes after placement along south beach during maximum flood tide under the following prototype conditions:

Table 2.2:1!




Reference wave height = 8 feet
Wave period = 12 seconds
Reference wave angle = 31 degrees from north
Water elevation: + 8.0 feet
Beach level: Normal
Note: An asterisk (*) bef ore an entry denotes that float passed into the inlet during the experiment, in
which case the elapsed time of travel is noted.
Initial Float Position (Model template
Float 29.0 28.0 27.5 27.0 26.5 26.0 25.0
1 10.5 24.5 2.0 1.5 2.0 3.0 2.0
2 3.5 18.0 2.5 1.0 3.0 3.0 2.0
3 2.5 6.5 5.5 2.5 3.5 2.5 1.5
4 2.5 26.0 15.0 6.0 3.0 2.5 1.0
5 3.5 2.5 6.5 1.0 2.5 2.0 2.0
6 5.5 4.5 3.0 1.5 2.0 3.0 2.0
7 7.5 5.0 3.5 2.0
8 9.5 4.0 2.0 2.0
9 3.5 4.5 11.0 2.5
10 4.5 2.5 3.0 3.0

Final positions (given in terms of physical model
template numbers) of spherical floats two minutes after placement along south beach during maximum flood tide under the following prototype conditions:

Table 2.3:




Reference wave height = 8 feet
Wave period = 12 seconds
Reference wave angle = 31 degrees from north
Water elevation: + 8.0 feet
Beach level: Nourished
Note: An asterisk (*) before an entry denotes that float passed into the inlet during the experiment, in
which case the elapsed time of travel is noted.
Initial Float Position (Model template
Float 29.0 28.0 27.5 27.0 26.5 26.0 25.0
1 2.5 3.0 2.0 2.0 2.5 2.5 3.5
2 2.5 4.0 3.5 3.5 5.5 2.5 2.5
3 3.0 5.5 3.5 3.0 1.0 3.5 3.5
4 7.0 4.5 3.5 2.0 3.5 6.0 4.0
5 2.5 9.5 2.5 4.0 6.0 3.5 2.0
6 5.0 9.0 2.5 7.5 3.0 2.5 2.5
7 6.5 19.0
8 0:12 3.5
9 0:12 17.0
10 4.5 2.5

I I

Final positions (given in terms of physical model template numbers) of spherical floats two minutes after placement along south beach during maximum flood tide under the following prototype conditions:

Table 2.4:




storm waveiconditions were also accompanied by the design stormelevated sea level of +8.0 feet prototype, while the normal conditions were run at MSL.
Table 12.1 shows the test results for normal wave conditions and the typical shoreline configuration. It is apparent that all floats released north of model template 26.5 moved into the inlet during the course of the experiment. Floats released at template 26 showed mixed or little motion while all floats released at template 25 were observed to move downcoast (south).
For the identical wave conditions but with the nourished shoreline in place, the gross details are similar to the normal case with itwo notable exceptions (Table 2.2). The extent of influence of the flood current has been increased, as now all the floats released at template 26 moved upcoast (north), with a majority of these entering the inlet. Note also that the travel times for the floats at templates 27 and 26.5 to reach the inlet are significantly lower than in the first case. The large majority of the floats placed at template 25, however, still moved downcoast. The second difference is that of the floats placed at template 29 (adjacent to the south jetty), only six (60%) actually entered the inlet. The remainder were observed to hold in a "dead space" created in the wave shadow of the jetty for the duration of the experiment. Note however that almost every float placed between template 28 and 27 entered the inlet, the majority doing so in under 30 seconds.
Table 2.3 gives results for the normal shoreline configuration under design storm conditions. Note that in this case all floats moved downcoast regardless of position, and that the travel distances are quite large compared with the normal wave conditions (majority of floats moved beyond template 5, i.e. over 20 feet displacement in the model). A similar set of results is found for the nourished beach configuration under storm conditions (Table 2.4), although 2 of the 10 floats placed at template 29 were observed to enter the inlet. The remainder of the floats moved downcoast with a speed similar to the normal beach case. It should be noted that in both these experiments the storm tide level was




above the jetty crest elevation, such the waves would break and pass over the jetty, thus reducing the diffraction shadow zone.
This series of experiments will be repeated in order to test
the effectiveness of any possible design modification (particularly lengthening) of the south jetty aimed at reducing the flow of south beach sand into the inlet. Moreover the results of these physical model tests and the original field tracer studies suggest that it may be useful to explore alternative means of placement of beach
nourishment material on the south beach, such as a reduction of the proportion, of material placed in the 300-foot zone immediately south of the south jetty. This may aid in reducing the passage of
nourished beach material into the inlet under a variety of wave conditions,! thus reducing the need to pump the same material twice and increasing the efficiency and capacity of the passive trap bypassing system currently employed.
2.3 Longr-Term Loncrshore Transport Simulations
It has been shown (Mehta et al., 1991a) that the longshore transport of sand is an episodic process that can be potentially dominated by a few maj or storm events. Such events are quite important when considering design options, and are only predicted
through a statistical description of the transport process. A
statistical model of the longshore drift based on WIS hindcast data has been 'developed accordingly to account for the seasonal variations in transport rates and direction. Since the 20-year hindcast transport populations have been shown to be largely lognormally distributed, monthly means and standard deviations of the logarithmically transformed distributions of northward and southward transport have been calculated. The transport is thus statistically represented by six parameters: the monthly mean and standard deviation for northward and southward transport and the percentages of time during the month that the transport is in each direction.
A daily synthetic data generation process is followed to produce transport simulations of any length (an effective maximum
of 20-year record length is imposed since this is the length of the




original data set). A random number is selected to establish the direction of transport for a given day, based on the calculated percentages. The appropriate transformed normal distribution (northward or southward) for that month is sampled to yield a daily transport. The process is repeated for as long as necessary.
With such a process, 5 year synthetic transport simulations were produced in Mehta, et al. (1991b), which showed both the episodic nature of the transport process and the benefits of dredging sand for nourishment of the south beach prior to the "nonpumping" window for turtle nesting rather than after it. For
complete evaluation of the effects of natural variability over the design period, the statistical model was used to generate several realizations of 20-year longshore transport data. These values were used together with the sediment budgets of Mehta et al. (1990a) and (1991b) to predict the accumulation of nourished sand on the south beach under several 20-year simulations, examples of which are given in Figs. 2.2-2.4. The datum for the sand volume is chosen as :a "critical" level of sand at which nourishment is considered crucial. In this way the simulation begins with the inlet (JID) sand trap empty and the total dredged volume of sand in place on the south beach. In each case the dredging is performed once a year over a 20-day period in March, prior to the non-pumping window (which was previously shown to be more beneficial than dredging after the window). The dredged volume for each simulation is 45,000 'cubic yards, which is approximately the sand volume required according to the basic sediment budgets.
Figure 2.2 shows a simulation in which the south beach does not exceed the critical erosion level (i.e. negative volumes) over the entire 20 year period. The standard pattern of very low transport during the summer following dredging (steep upward slope followed by a flat section) and high erosion over the winter months (downward slope) is repeated every year, but the dredging rate is sufficient to maintain the beach. Figure 2.3 however, shows an equally feasible realization from the same statistics in which the critical erosion level is exceeded for the majority of the 20-year simulation, in some cases by over 25,000 cubic yards. This shows




the importance of the natural variability in the sediment transport process. The episodic nature of the transport is again seen in Fig. 2.4, in which the beach is maintained in a favorable condition for almost the entire 20-year period until a single large transport year causes the sand volume to nearly deplete to the critical level. In summary, for a series of realizations from the same set of transport statistics, the budget-derived dredging rate of 45,000 cubic yards per year permits critical erosion to occur on the south beach in five out of ten instances. This indicates that in order to avoid situations such as those shown in Fig. 2.3, an annual bypassing capacity of greater than 45,000 cubic yards (e.g. 60,000 cubic yards) must be maintained.
These statistical simulations have been performed to provide a means to analyze the trap-dredge system currently in operation at Jupiter Inlet. Any other promising alternatives, such as
continuous bypassing systems with a limited or variable storage, can also be effectively simulated in a similar manner. On a long term basis however, the results shown above are also applicable (in general) to such other bypassing options.




Wave Directicn

I
Time Line SILE

#29
1 foot spacing

Normal Shoreline/

I
Nourished Shoreline

Model Template #19

Fig. 2.1 Approximate inlet and shoreline configuration and
model template lines for physical model drogue
studies.

#27 #25
#23

IN= -




ACCUMULATED SAND ON SOUTH BEACH

TIME(DAY)PRETIME (DAYrS)

Fig. 2.2

20-year longshore transport simulation with annual dredging of 45,000 cubic yards showing volume of nourished sand on south beach with no critical shoreline recession.

100000 ?5000 50000
0
- 25000
-50000
-75000
-100000




ACCIJHUMULATED SAND ON SOUTH BEACH

100000 7 S000

50000 25000
0
-25000
-50000
-75000
-100000

PRE-HINDO
TIME (OATS)

Fig. 2.3 20-year longshore transport simulation with annual dredging of
45,000 cubic yards showing volume of nourished sand on south
beach with substantial shoreline recession beyond critical
levels.




ACCUMULATED SAND ON SOUTH BEACH

100000 75000 50000 25000
0
-25000
-50000
-7S000
-100000

TI ME (DAYS) PRE-INo00

Fig. 2.4 20-year longshore transport simulation with annual dredging of
45,000 cubic yards showing volume of nourished sand on south beach with near-critical shoreline recession due to a single
large transport year.




III. INLET NEARFIELD

3.1 Introduction
In this chapter we discuss issues related to the exterior region of Jupiter Inlet including the feasibility of a dredged offshore channel, and issues related to possible mining of the ebb shoal. Study is continuing in these areas; hence progress to date
only is mentioned. The exterior region is being modelled via a previously described numerical model and a physical model, in which jetty modifications to improve navigation and reduce sand influx are currently being tested as well (for prior reference see Mehta
et al. 1990b; 1991a) Available results from these models and prior experience (e.g. form other studies) are used in making the following observations.
3.2 Waves in the Study Area
Since decisions concerning for example the offshore navigation channel depend upon the ability to reproduce the existing wave climate in the study area, in what follows we present estimated wave heights at three selected near shore locations under variable water levels, inlet tidal flows and wave directions. These stations, S2, S3 and S6 are shown in Fig. 3.1. Additional stations
from this figure are referenced later. In Table 3.1 wave heights at S2, S3 and S6 are plotted as percent of reference wave height at a station northeast of the inlet where the depth of water is 25 ft.
The flood and ebb flows correspond to a reference tidal velocity of 3.61 fps in the inlet channel. The two directions of approach are NE and SE. Two water levels are considered: msl (present) and +8 ft
(NGVD) design level based on discussion presented in Chapter V. Reference wave height and period are related to the water level; at
msl the values are selected to be 4 ft and 8 sec, respectively, and at +8 ft they are 8 ft and 12 sec, respectively.
Note from Table 3.1 that, as expected, the +8 ft storm surge condition is the most severe one regardless of the wave direction or the stage of tide in the inlet. Severity here is considered in
terms of reduction in wave height; lesser the reduction the greater 34

I I




Table 3.1: Wave heights at Stations S2, S3 and S6 obtained by mathematical model simulations
Tide Water Wave Wave Height (%)c at
Level (ft) Direction S2 S3 S6
Floodd 0a NE 36 76 64
Flood +8b NE 86 70 93
Ebbd 0 NE 34 75 63
Ebb +8 NE 91 77 99
Flood 0 SE 26 70 41
Flood +8 SE 101 106 106
Ebb 0 SE 25 55 43
Ebb +8 SE 85 88 102
amsl(NGVD).
bDesign storm surge level.
Percent of reference wave height measured at the 25 ft contour northwest'of the inlet. Reference wave height and period are varied with water level. At msl they are selected to be 4 ft and
8 sec, respectively; at +8 ft they are 8 ft and 12 sec, respectively.
dInlet channel reference velocity is 3.61 fps.
will be the impact. Note that in some cases there actually is wave amplification (> 100%).
In Table 3.2 a comparison is presented for the wave height (%) at station' S2 using results from the physical model and the mathematical model. Given the possible sources of error in both type of modeling approaches, the agreement for the four conditions tested may be considered to be acceptable, and lends confidence to both approaches in terms of their predictive potential for testing the impact of modifications.
In Figs. 3.2 and 3.3 numerically simulated ebb and flood current patterns are shown under the following conditions:
reference wave height 1.21 ft and period 4 sec, waves from the SE direction and a reference inlet velocity of 3.61 fps (1.1 m/sec) (flood as well as ebb) corresponding to occasionally prevailing conditions during summer (see for example Mehta et al. 1991a for a
35




Table 3.2: Comparison of wave heights (from NE) at Station S2
between mathematical and physical model simulations
Tide Water Wave Height (%) at Station S2
Level (ft) From Physical From Mathematical Model Model
Flood 1 0 43 36
Flood +8 89 86
Ebb 0 25 34
Ebb +8 118 91

description of the prevailing conditions during a summer 1990 field study).
3.3 Offshore Channel
Referring to the proposed 100 ft wide and 10 ft deep (msl) eastern and southeastern channel alternatives in Fig. 3.1, the corresponding capital dredging volumes are given in Table 3.3. Note that we have selected four different surveys of the same area obtained at different times to highlight the likely range of variability of the dredged volumes. The southern channel is longer with greater volumes, although it should be emphasized that capital volumes shed no light on the likely rates of infilling of these two channels. Transport calculations are presently being carried out to provide an answer to the question of infilling rates, which will essentially determine which of the two channels, if either, is a better or a viable option.
Note for example that the volume of capital dredging in the southeastern channel varies by as much as a factor of 4. We attribute this variability to natural variations in the bottom conditions in this area. These variations in turn are indicative of the mobile nature of the ebb shoal, whose configuration and volume appear to change seasonally. For a comparison of contours from March'79, August'79 and February'80 surveys see Fig. 4.1 in Mehta
I




Table 3.3': Estimated capital dredging volumes in the proposed
channel alternatives as functions of bathymetry
Channel Bathymetry
May '79 Aug '79 Feb '80 July '86
(yd) (yd) (yd) (yd)
Eastern 9300 10400 11500 6600
Southeastern 15800 33000 19700 8400

et al. (1990a). Volumetric calculations are given in the next section.
3.4 Ebb Shoal Volumes
Table13.4 gives six calculations of the ebb shoal volume at
Jupiter inlet. Note that ebb shoals of the type here considered are features that are distinctly associated with tidal inlets (Bruun, 1978). Their position and size (given sufficient sand supply from
the beaches and the littoral drift sources) are contingent upon the wave energy and the tidal energy. Thus when a new inlet is opened, initially there is a rapid growth of the shoal, the rate depending upon the prevailing hydrodynamic conditions, inlet size and sand
supply. This initial phase can vary from a few months for tiny beach inlets to decades for very large ones. Later the growth rate
will slow down and in fact, since the balance of f orces due to waves and tides changes continuously, the ebb shoal will respond to these changes by varying its size and configuration, without ever quite reaching a genuine equilibrium. In terms of time-scales of variability, one can conceive of monthly or seasonal effects superimposed on more long term variability. When the inlet closes
naturally or is closed artificially, tidal action is cutoff and there is a general tendency for the sand to move to the shore and then moving along it, thus becoming a part of the littoral drift. The shoreline eventually reverts to one with prevailing beach and bottom contours as would occur in the absence of the inlet. Thus the ebb shoal volume is calculated as the volume in excess of the




Table 3.4: Ebb shoal volumes at Jupiter Inlet
Year 1883 1957 1967 1978 1980 1986
Volume
(M yd3) 0.9 0.3 1.0 0.4 0.4 0.9
Plan area
(M yd2) 0.5 0.9 1.9
Controlling
depth (ft) 2 3 4 4
Seaward contour
of influence 22 18 18 28
Longshore extent to influence
(x 1000 ft) 3.2 6.6 4.0 6.4
NOTES:
a) A narrow tongue-like submarine spur extending seaward from the
10 ft contour (about 1,500 ft from the jetties) is noted in
the 1957 hydrographic survey.
i
b) A submarine trench with its head at the 20 ft contour (about
5,000 ft from the jetties) and extending seaward is noted in
the 1986 hydrographic survey.
c) Inlet was closed from 1942 to 1947. This may explain the low
volume in 1957.
d) Between 1947 and 1977, 1.1 M yd of material were dredged from
the inlet and placed on the southern beach. Half of this material came from the construction of a sand trap, 1,000 ft
west of the inlet mount, in 1966.
e) Sources of computed volumes:
1883: Marino & Mehta (1986)
1967: Dean & Walton (1976)
1978: Marino & Mehta (1986)




bottom contours in the absence of the inlet. Such contours are usually found both updrift and down drift of the inlet (Dean and
Walton, 1976). At Jupiter the calculation of ebb shoal volume using this approach is straightforward. In other places where for example two adjacent inlets influence each other, as in the case of St. Mary's Entrance and Nassau Sound, "inlet-free" bottom contours are not easily located and assumptions concerning their configurations have to be made (Marino and Mehta, 1986).
The effect of changing the long term "balance" between wave energy and tidal energy on the ebb shoal can be significant. This
change can! be brought about by changing the wave energy or the tidal energy. At Matanzas Inlet on the east coast of Florida, a dike in the interior waters was constructed in 1976, which
temporarily reduced the tidal prism through the inlet. The ebb shoal responded quite rapidly; within months it approached the shoreline and the controlling depth over it was reduced. This caused the waves to break more vigorously over the shoal, with reduced wave action in the lee of the shoal. Furthermore, it appeared that the blocking effect of the ebb shoal might in fact
close the inlet entirely. Eventually, however, the tidal prism increased and the shoal reverted to its initial position (Mehta and Sheppard, 1979). If the inlet is closed in an area where the littoral drift predominates in one direction, the sand from the ebb shoal will be largely transported in the direction of the drift. At Captain Sam's Inlet in South Carolina, the channel was deliberately closed so as to allow the ebb shoal to move onto the downdrift beach of Seabrook Island, where the beach required nourishment (Kana and Mason, 1988).
The ebb shoal volume data in Table 3.4 unfortunately are not evenly spaced in time, and therefore cannot yield any information
on the time-variability of the ebb shoal of Jupiter Inlet. Nevertheless it is interesting to note that the volume (. 0
yd) in' 1883 is consistent with that in 1967 and in 1986, while the volume in 1957 is in approximate agreement with that in 1978 and in 1979, although the low value in 1957 was possibly due to the fact that the inlet was closed during 1942-47. This comparison and the




nature of time-variability as gleaned from these meager data nevertheless suggest that the ebb shoal is mature (i.e. it is not is a consistent growth mode) and that the observed variability in
volume is associated with corresponding variability in the wave climate.
A recent study of several inlet ebb shoals along the Gulf Coast of Florida (Gibeaut, 1991) in fact indicates a significant dependence of the ebb shoal on wave climate; when wave activity is high the volume is small and vice versa. Undoubtedly along the Florida east coast hurricanes, northeasters and winter waves largely determine ebb shoal volume at a given inlet. In Fig. 3.4 a
19 year record of the wave energy (per unit surface area) is plotted using hindcast data from the Corps of Engineer's Wave Information Study (WIS) (Thompson and Jensen, 1989). Also plotted are two ebb shoal volumes that were measured during this period. Even though two data points are not enough to arrive at definitive conclusions, it is observed that the observation of Gibeaut (1991) regarding the relationship between the volume and wave energy is corroborated. What is implied from these observations in general is that when wave action is high, sand stored in the inlet feeds the beach, while under attenuated wave activity the reverse occurs, i.e. sand piles up in the ebb shoal. In turn this means that the variability in the ratio of wave energy to tidal energy is quite important in governing ebb shoal dynamics (Bruun, 1978), and furthermore this natural process of sand exchange between the ebb
shoal and the beach is very important to the stability of the beaches adjacent to the inlet during times of intense wave action.
Consider the 1967-78 situation in Table 3.4, during which (ignoring volumetric changes that undoubtedly took place during that interval) the ebb shoal "returned" 10x06-0.4 X16-0.7 X 106 y3 of sand to the beaches. In 1978 the alongshore extent of influence of the ebb shoal was 6,600 ft (Table 3.4). Taking a 500 ft wide bea ch, the returned sand would form a 5.7 ft thick layer on the beach. over the 6,6000 ft length. This very approximate calculation illustrates the significance of the inter-relationship between the beach and the ebb shoal.
40




The precise mechanisms by which ebb shoal responds to tide and wave action is imperfectly understood. Consider for instance the
i
controlling !(i.e. minimum) depth over the ebb shoal in Table 3.4. In spite of the over three fold variation in the volume between 1957 and 1986 the controlling depth remained "practically" unchanged, varying between 2 and 4 ft. While this is indeed a twofold variation, no major gap in the ebb shoal which would change the transmission of wave energy to the beaches occurred. This observation, coupled with data on the variability of the plan area of Gulf Coast ebb shoals with wave energy presented by Gibeaut (1991) suggests that ebb shoals have a tide-controlled portion close to the shore and a wave controlled portion seaward. Variation in wave action causes the wave-controlled part to vary, with lesser change in the tide-controlled portion; the controlling depth occurs in this tide-controlled portion. The change in the wave-controlled seaward portion with wave action would be reflected in the seaward extent to which the ebb shoal influences the offshore bottom contours. Indeed this is seen from Table 3.4. The extent of influence of the ebb shoal did vary; the minimum being the 18 ft contour and the maximum being 28 ft. The relationship between this description of tide-dominated, stable shoreward portion of the shoal and wave- controlled, more ephemeral seaward portion, and the description of the ebb shoal as composed of "active" and "passive" portions in quite the opposite sense (Mehta et al. 1990a) is not quite clear.
Some apparent discrepancy also exists for instance between the 'results of Walton and Adams (1976) and the recent observations of Gibeaut (1991). While the former investigators found the ebb shoal volume to increase with decreasing wave energy, Gibeaut found the opposite trend when he compared tide-controlled ebb shoals with ebb shoals in mixed tide/wave environment, and attributed the difference in the trend by considering the tide-controlled ebb shoals !to be in the growing mode, with considerable additional
capacity to store more sand in future. While this explanation seems plausible, it underscores the need for better understanding of the dynamics of ebb shoals.




3.5 Minin4 of Ebb Shoal
The inlet ebb shoal, while an integral component of the inlet
system, is 'an obvious source of sand for beach nourishment. Mining here implies dredging to meet the needs well beyond what may be necessary to offset any uptake of littoral sand by the ebb shoal on an annual basis. For this definition of "mining" one could choose
a decadal basis or longer, but such a basis can not be justified in terms of any sediment transport cycle, which is primarily tied to the solar year even though admittedly there are longer term cycles
present in astronomically controlled phenomena, e.g. the 19 year metonic cycle of tidal variation. Mining of ebb shoal has been carried out at Redfish Pass (Tackney, 1983) and Boca Raton Inlet (Coastal Planning, 1991), and has been proposed for New Pass and Longboat Pass. Undoubtedly in years to come more ebb shoals may be dredged.
As opposed to mining to nourish a downdrift beach which is a relatively new concept, dredging of the ebb shoal to maintain an offshore navigation channel has been conventionally carried out, and when the dredged material is placed on the beach it amounts to mining in the same sense as noted. A number of Federal Navigation
Projects in Florida fall in this category. Traditionally however the possibility of an unacceptable level of beach erosion was never a paramount issue until recent decades. It is now recognized that
about 80 % of all beach erosion in Florida over the past century is attributable to inlets (Dean, 1988). This erosion is largely
confined to the downdrift shoreline, since updrift of the inlet accretion occurs. In fact, on the average, the shoreline of the east coast of Florida has actually accreted at the rate of 0.78 ft per year over the past century (Dean, 1991).
Consider the channel along an easterly alignment shown in Fig. 3.*1. The proposed dimensions for this channel are 100 ft width X 10 ft depth. The capital dredging volume required for this case using for example the 1986 bathymetry would be 6,600 yd3 (Table 3.3). one can conceive of wider and deeper, geometrically similar channels as follows: 150 ft x 15 ft, 200 ft x 20 ft and 260 ft x 26
ft (depth at Fort Pierce Inlet offshore channel). Fig.: 3.5 shows




the variation of capital dredging volume required with channel cross sectional area. Note the dramatic increase in volume with area. If for example a channel with a cross sectional area of 5,400 ft' were to be dredged, 150,000 yd3 of sand would have to be removed. This would be a rather large (e.g. 250 ft x 21.6 ft) channel for Jupiter, although smaller than those at neighboring entrances (Fort Pierce: 350 ft x 26 ft; Palm Beach: 350 ft x 31 ft). There does not seem to be any justification on grounds of navigation to create such a wide and deep channel at Jupiter. Furthermore, such a channel wound undoubtedly interfere with the smooth flow of sand, and would have to be regularly dredged with
the dredged material placed downdraft to manage navigation as well as beach erosion. We do not recommend cutting a large channel through the ebb shoal either for navigational purposes or as a means to mine the ebb shoal for beach nourishment.
Mining of offshore sea bed, its potential impact on the shoreline and related policy matters have been issues Europeans have had to contend with for decades. In 1976 for example 11 % of the total sand and gravel production in the U.K. was derived from offshore deposits (Price et al., 1978). Along the south coast of England, for example, the approximate limit for onshore/offshore movement of sediment, i.e. the depth of closure, is considered to
be 10 m, and mining in shallower areas is restricted. Another criterion used in U.K. is a distance of 600 m as the limit within
which mining is restricted. Along the east coast of Florida the depth of closure is considered to be around 25-27 ft or about 8 m. The application of a similar criterion as in U.K. in terms of the
depth of closure would severely restrict offshore mining, since for example it would include almost the entire ebb shoal and adjacent areas at Jupiter (Fig. 3.6). It is our opinion that such a rigid criterion is uncalled for as far as Florida is concerned, and that it seems opportune to study the issue of offshore sand mining in Florida on i a generic basis, and then to develop engineering criteria that would assist in making case by case evaluations. At present the lack of sound criteria for deciding upon the extent to
43

I I




which an ebb shoal should be mined, if at all, causes much public aggravation on both sides of the issue of whether or not to mine.
The conventional approach to determine the potential impact of mining on the shoreline is via f ixed bed numerical or physical models. In such models the area to be mined is "excavated", and the corresponding impact evaluated in terms of wave related parameters. Palm Beach County for example has decided upon the aerial configuration of the borrow area shown in Fig. 3.1, based on the
results of mathematical model studies which showed no significantly adverse shoreline impact, assuming there would be no natural rearrangement of the bottom material. A total of 500, 000 yd3o sand are proposed to be dredged. In Table 3.5 we present wave height information obtained mathematically to illustrate potential effects of modifying the offshore bottom under a +8 ft storm surge, 4 ft high, '8 sec period reference offshore waves arriving from SE. The inlet condition is flood at 3.6 fps velocity. We have chosen the +8 ft elevation as it represents an extreme event situation, but have deliberately chosen a 4 ft wave height which is
considerably (-50%) lower than anticipated extreme, with a 8 sec (as opposed to 12 sec) period, to consider a non-extreme
combination of parameters. Wave height ratios are calculated to better illustrate the effects of modification (represented by height Hffo) relative to existing conditions (Hexist). Station locations refer to Fig. 3.1. Note the rather minor effect of the Southeast channel on wave action everywhere. The same can be said f or the eastern channel, at least under the selected reference wave and inlet flow conditions. With the ebb shoal mining, wave heights will decrease or increase depending upon wave refocussing due to bottom mod iification. This would be expected and consequently
indicates that the bottom sediment will redistribute itself. Indeed ebb shoal mining will influence the bottom conditions much more significantly than say the dredging of the proposed southeast channel.
Is this effect detrimental to the beach? To look at this question we present calculations of wave height ratios in Table 3.6, comparing conditions at the same seven stations as in




Table 3.5:

Wave heights at several stations obtained by mathematical model simulations under existing and modified conditions'

Condition Wave Height Ratio, HJ/Hxist
A2 B7 C4 S2 S3 S4 S6 Existing 1.00 1.00 1.00 1.00 1.00 1.00 1.00
Southeast Channel 1.00 1.00 1.01 1.00 1.01 1.05 1.01
i
Eastern'Channel 1.00 1.00 1.00 0.99 0.85 1.07 1.00
I
Ebb Shoal Mined 1.67 0.74 1.37 0.48 0.43 1.14 1.29
aWater level +8 ft (NGVD), reference (offshore) wave height 4 ft, period 8 sec, SE inlet flood flow (3.6 fps velocity).

Table 3.6:

Wave heights at several stations obtained by mathematical model simulations using different bathymetric surveys

Survey Wave Height Ratio, Hsurvey/H198
A2 B7 C4 S2 S3 S4 S6
1986 1 1 1 1 1 1 1
1979 0.93 0.90 0.79 1.00 1.45 2.35 1.13
1980 0.94 0.88 0.81 1.04 1.18 1.56 1.13




Table 3.5,1 by selecting different bottom surveys (but without dredging the borrow area) Here H1986 refers to wave height calculated using the 1986 survey, while H survey is equal to H196, H1979 or H 1980.* Co imparing the results with those in Table 3.5 indicates that, in general, wave height changes due to ebb shoal mining in its initially established position would not be more drastic than changes that seemingly occur due to natural variations in the ebb
shoal size and configuration. Therefore, as such these calculations are not at variance with those carried out by Palm Beach County. They do however highlight one important fact, namely that the ebb shoal is quite mobile and therefore that its mobility does
measurably influence wave heights in the inlet area. Note that since the wave energy is proportional to the square of the wave height (for a given wave period), changes in wave height significantly amplify changes in sediment motion which is related to corresponding changes in wave energy. Thus the main difficulty we see with regard to results such as those presented in Tables 3.5
and 3.6 isi that they do not account for dynamic changes in the bottom bathymetry, and in turn therefore cannot account for any episodic rearrangement of the bottom, e.g. due to a hurricane.
It is well established that major hurricanes can indeed alter the bottom !conditions in a "catastrophic" way, e.g. Hugo in 1989 in South Carolina. In Florida we have been fortunate in recent decades especially along the East coast; we have not had for example the
devastating effects of Dora in 1964. As a rule of thumb, in the "shallow" areas waves break at water depths which equal the wave height. The ebb shoal, by its very presence, undoubtedly protects
the beaches in the inlet area from onslaught of large waves. We should avoid operations that may reduce this protection since we have no control over natural oceanic phenomena.
Referring to Fig. 3.6, whether a part of the ebb shoal would
"sluff"! into the "hole" is an effect to content with, but one which is difficult to predict. Note that the figure, even though schematic, presents a highly distorted cross sectional view; actual slopes at the edge of the hole could be considerably milder, e.g. 1:3 to 1:8; it would therefore be inappropriate to assume that




sluffing will indeed occur based on visualization of Fig. 3.6. Also, we are unable to predict whether the ebb shoal in the coming years will be in a growing mode or a shrinking mode, since that will depend on the corresponding weather patterns, including
hurricanes'and storms. In the growing mode, the shoal will trap "new" sand, while giving up sand in the shrinking mode. Given this dynamical condition, it would be inappropriate to use a long term
sediment budget, such as the one developed in this report, for ascertaining the refilling rate of the hole. The hole may refill rapidly, e. g. in 2-5 years, or may not refill for decades.
Given these observations we are of the opinion that a "nothing will happen" scenario relative to potential effects of ebb shoal
mining cannot be developed on rational grounds, since we are limited by our present day technological ability to predict weather patterns and their effect on sediment motion at Jupiter Inlet. While we consider the mining of ebb shoal in general as an acceptable and indeed welcome option within the rubric of technological solutions for beach nourishment, we wish to express serious reservations over the plan to mine 500,000 yd3 specifically from the Jupiter Inlet ebb shoal, particularly because the total volume of the sand stored in the ebb shoal (not including material below the ebb shoal as defined here) has at times been less than the total amount proposed to be dredged. We recognize that there may be no direct connection between the volume to be dredged and the ebb shoal volume since additional sand resides underneath the shoal as well. However, we are concerned that in the event of not highly likely but entirely possible episodic or catastrophic
rearrangement of the bottom, if the shoreline were to become exposed to storm wave action, the damage to shoreline could considerably outweigh the advantages gained by mining the ebb shoal to the extent proposed.
To propose an alternative mining site or to determine how much mining should be allowed there is beyond the scope of this study.
We do wish to note however that cumulative coastal engineering experience' strongly suggests that we take actions to modify our coastal environment gradually, carefully monitoring the impacts.
A 7




operations 'that might lead to irreversible consequences should undoubtedly be avoided. A possible mining scenario at the Jupiter
Inlet site could be one involving mining of say 150,000 yd3 of sand (equivalent to a good-sized navigation channel) from the southern end (which is most distant from the inlet) of the proposed borrow area, and monitor the ebb shoal plus the neighboring beaches for a
period of two years to record impacts if any. If however the additional 350,000 yd3 are required immediately, a source for the same may be searched for in the area immediately south of the proposed borrow area in about the same water depth, or elsewhere.
An approximate basis for the 150,000 yd3 quantity noted is as follows. Elsewhere in this report (Chapter VI) we have determined a long term annual sedimentary budget for the inlet (see e.g. Fig.
6.13), which indicates that a total of 7,000 yd3 of sand is dispersed and therefore "lost" in the interior waters of the inlet, while another 7,000 yd3 are transported offshore. Thus the presence of inlet apparently reduces the net annual littoral drift rate by
14, 000 yd3. This value is 6% of the net drift rate which is small and subject to some error for reasons cited. Nevertheless, assuming its robustness, one obtains 140,000 yd3 as the amount "lost" due to the presence of the inlet over a 10 year period. This amount is close to 150,000 yd3. Thus on the basis of this approximate calculation, mining of the ebb shoal should be restricted to 150,000 yd3 per decade, unless post-dredging monitoring studies and other considerations indicate otherwise.




Proposed

OA10 C
Proposed G5
East Channel
o C3 Proposed
Southeast
S2 Channel
S1 *S6
-00
....~C SS 3 ..: iiii:j iiii ...... ..... ....................i
Fig. 3.1 Proposed alternative offshore channel alignments and sand borrow area, and wave
measurement stations in the physical and mathematical models.




Fig. 3.2 Numerically simulated ebb flow pattern near Jupiter
Inlet; reference wave height is 1.21 ft, period 4 sec, direction NE and inlet velocity 3.61 fps (1.1 m/sec).
50




Fig. 3.3

Numerically simulated flood flow pattern near Jupiter inlet under same conditions as in Fig. 3.2.




C\1
E
E
z
cc:
C-)
CC
ci:
I
U
z

1958 1960 1962 1964 1966 1968 1970 1972 1974

Fig. 3.4

YEAR
Offshore wave energy over a 19 year period in the Jupiter Inlet area, and ebb shoal volumes.

4000 3500 3000 2500
2000 1500 1000 500

1.2
AA
1.0
U)
x 0.9 0
I
0.8 <
0.7 C:
0.6
0.5 =
0.4
.
0.32
0
0.2m
CL

0 L. 1956




CHANNEL C.S. (ft2)

Fig. 3.5

Capital dredging volume required as a function of design eastern channel cross section at Jupiter Inlet using 1986 bathymetry.

0
w
w
M
0
w
-j

103

104




---7
Inlet Channel

Beach Profile Without Ebb Shoal

Area to be' Mined

Fig. 3.6 Schematic of ebb shoal and area of mining.




IV. INLET INTERIOR MODELING

4.1 Introduction
This progress report presents the results from the sediment transport modeling (using a two-dimensional depth-averaged finite element model) of the Loxahatchee River estuary. The objectives achieved in this effort to date include:
(a) calibration of the hydrodynamic and sediment transport models;
(b) estimation of net sediment fluxes pass (i.e., to the west of)
the Florida East Coast Railroad and the US 1 bridges, into the inlet,! the gross sediment fluxes at the inlet mouth, and the average sedimentation rates in the marina on the south side of the river for selected median grain diameters, D50 = 0.20 mm
and 0.150 mm.
The sediment transport model, described in more detail in Mehta et al. (1991a), predicts the two-dimensional (depth-averaged) velocity and salinity fields, and the change in bottom elevation due to scour or deposition resulting from sand transport at the nodes comprising the finite element grid.
4.2 Model Application
The finite element grid of the Loxahatchee River estuary used in the sediment transport model is shown in Fig. 4.1. The grid was expanded from that given in Mehta et al (1991a) to include the inlet nearfield region. The grid is composed of 963 quadrilateral elements and 3193 nodes. The size of the elements was varied such that the highest density of nodes occurred in the areas of expected high spatial velocity gradients (e.g., in the proximity of the jetties). The same water boundaries in the Loxahatchee River indicated in Fig. 6.6 in Mehta et al. (1991) were used in the new grid. The new ocean boundary consists of the outer semi-circular arc. These water boundaries were chosen because of their proximity to tide gage stations used during a study in 1976 by the University




of Florida (Chiu, 1975) and because of their proximity to NOS secondary tide stations.
Initial conditions used in the hydrodynamic module were zero velocity and constant water surface elevation at all nodes. Boundary conditions used for the hydrodynamic module consisted of the NOS predicted water surface elevations at the specified water boundaries for the period March 1 30, 1991. The predicted tide for the ocean boundary nodes for this period is shown in Fig. 4.2.
Calibration of the sediment transport module was performed by matching the predicted sedimentation rates in the Jupiter Inlet District trap and the U.S. Army Corps of Engineer trap with the available dredging records. Because of the extremely high CPU times required to run the model to simulate an extended period of
time (e.g.,' months-to-years), the model was run, using a 300 second time-step, for only the 30 day period indicated above. Such a
small time-step has been found to be necessary for the sediment transport module. The predicted sedimentation rates for the two traps over the 30 day period were then extrapolated to the period of time between consecutive dredging operations assuming an exponentially decreasing (with time) rate of sedimentation.
4.3 Model Results
The estimated net sediment transport rates into Jupiter Inlet, west of the railroad bridge, and west of the US 1 bridge, and the gross transport rate at the inlet mouth for D5 0.20 mm and 0.50 mm are given in Table 4.1.
The average sedimentation rate in the vicinity of the marina
on the south shore was determined by averaging the predicted sedimentation rate at elements 401, 402, 407, 408, 413, 414, 419, and 420. The average sedimentation rate, with D5 0.20 mm, at these elements is estimated to be 16 cm/yr.
56




Table 4.1: Sediment fluxes in Jupiter Inlet channel

Location

D50 (MM)

Sediment Flux
(m3/yr)

Net/Gross

Jupiter Inlet US 1 Bridge Railroad Bridge

127,000 60,000 195,000 94,000

0.20 0.50
0.20 0.50
0.20 0.50
0.20 0.50

net net gross gross

3,300 1,400
1,800
800

net net
net net




Fig. 4.1 Finite element grid of the Loxahatchee River estuary.




Predicted NOS Tides at Jupiter Inlet
- used for ocean b.c.'s -

15
Time (days)

Fig. 4.2

Predicted tides at Jupiter Inlet for March 1-30, 1991, used for ocean boundary conditions.




V. STORM SURGE LEVELS

5.1 Introduction
Jupiter Inlet is located at the northern boundary of Palm Beach County on the eastern coast of Florida (Fig. 5.1). The adjacent counties on the north side and south side are Martin County and Broward County, respectively. Since Jupiter Inlet is situated very close to the boundary between Martin County and Palm Beach County, any weather information related to Martin County is very pertinent to the Jupiter Inlet area.
Estimation of maximum sea water level and the frequency of occurrence of various levels is essential for various purposes such as establishment of coastal construction control lines (Ref: 1), determination of areas inundated under storm conditions (Ref: 2), estimation of maximum wave runup elevation on beaches and coastal structures,' design of crest level of critical coastal structures, estimation of the extent of beach erosion during storms, and so on. The estimation of maximum sea water level needs to take into account the storm surge due to wind stress and barometric pressure effects, astronomical tide and the dynamic wave setup which occurs primarily inside the wave breaking zone. This water level is often denoted as the "combined total storm tide".
The prediction technique consists of combining the available historical hurricane statistics with a set of numerical models in
order to simulate the storm conditions at the site of interest. Some climatological characteristics of hurricanes and tropical storms on the Gulf coast and East coast of the United States are given by NOAA (Ref: 3). This report gives data on the frequency of landfalling hurricanes and tropical storms, probability distributions of central pressure, radius of maximum winds, speed and direction of storm motion; and also the joint probability of
these parameters. Data on storm tracks are also given in the Technical Data Report, Hurricane Evaluation Study for' the Lower Southeast Florida (Ref: 4).
Basedion the available data for the past several years, the storm surge level for Jupiter area has already been estimated by




different agencies. These estimates have been here reviewed and recommendations given on the magnitudes and corresponding frequency of occurrence of storm surge levels which may be adopted for studies such as the physical or mathematical model investigation of coastal problems related to Jupiter Inlet.
5.2 Martin County Data
Dean and Chiu (Ref: 5) have conducted frequency analysis of combined total storm tide for Martin County. The calibration of numerical model was based on the tidal data and high water marks caused by the hurricanes of September 1926, September 1945, September 1947 and September 1979. Varying friction characterized by vegetation, buildings and underwater areas was taken into account. The dynamic wave setup was based on analytical studies and wave tank tests.
Three transects located along Martin County shoreline were considered and five 500-year simulations for each one of the three transect lines were carried out on the computer. All data were plotted using the average value of the five simulations. The results of combined total storm tide frequency are given in Fig. 5.2. The same are also given in Table 5.1.
National Oceanic and Atmospheric Administration (NOAA) has conducted flood insurance study for Martin County, Florida (Ref: 6). The prediction is based on the data related to past hurricanes. The results of predicted storm tidal heights and the corresponding return period are given in Fig. 5.3. Salient data from this figure are presented in Table 5.2.
5.3 Palm Beach County Data
The National Oceanic and Atmospheric Administration (NOAA) has conducted flood insurance study for Palm Beach County, Florida (Ref: 7). Data on storm tracks for the Palm Beach County region were obtained from the data files of NOAA for the 100 year periods from 1871 to 1970. These tracks include three categories, including i) exiting hurricanes; storms that passed from land to the sea, ii) landfalling hurricanes: storms that penetrated the coast, and iii)




Table 5.1: Combined total storm tide values for various return periods, Martin County,
Florida (Ref: 5)

*Includes contributions from: wind stress, barometric pressure, dynamic wave setup and astronomical tides.

Combined Total Storm Tide Level* above NGVD (ft)
North Middle South

Return Period,
(years)

12.6 11.9
11.2 10.3 8.6 6.7

500
200 100

13.5 12.6 11.9 11.1 9.5 7.5

13.0 12.3 11.6 10.8 9.0 7.1




Table 5.2: Frequency of storm surge levels for Martin County, Florida (Ref: 5)
Return'Period Estimated Storm Surge Level (ft)
(Years) Northern Boundary Southern Boundary
500 10.5 10.2
200 9.2 8.8
100 8.0 7.7
50 6.8 6.5
20 5.2 5.0
10 4.0 3.8
alongshore hurricanes: storms that bypassed at sea. The hurricanes which affected Palm Beach County are listed in Table 5.3 (Ref: 7).
Twelve hurricanes passed through Palm Beach County during the 100 year period. Six of these entered the coast from the Atlantic
Ocean. The other six passed through Palm Beach County and moved into Atlantic Ocean. Generally, exiting storms do not produce high surges. In fact, exiting storms north of a location tend to lower the coastal water level due to wind setup effect. Hence only the storm tracks which are pertinent to Palm Beach County are shown in Fig. 5.4.
The analysis of storm tide frequency was based on the procedure laid down in the Weather Bureau Technical Report (Ref:
8). The characteristics of storms are described by central pressure depression,' radius of maximum winds, forward speed and storm direction. Each parameter was assigned appropriate probability of
occurrence.' Also, astronomical tides and bathymetry of continental shelf was taken into account while running the computer program for estimation of storm tides. The results are shown in Fig. 5.5. These are also tabulated in Table 5.4.
The mean tidal range at Palm Beach is 2.8 feet. Normal high
tide elevation in the Intracoastal Waterway ranges from about foot above mean sea level near Jupiter Inlet to about 1.5 feet near Boca Raton. The U.S. Army Corps of Engineers have estimated peak tidal




Table 5.3: Hurricanes affecting Palm Beach County, Florida 1871-1970 (Ref: 7)

Storm Date

Direction
(a) **

Direction
(b) **

Forward Speed (knots)

Principal Places in Florida Affected and Remarks

Oct. 30, 1876
July 2, 1878 September 1881 Aug. 16, 1890* Aug. 24, 1891* Aug. 2, 1898* Sept. 11, 1903* June 17, 1906

220 240 239 100 110 110
120 220

240 260 250 070 080
140 120 250

Southeast coast. Center of hurricane passed over northwestern portion of Palm Beach County.

14 Southern Florida. Center
through Palm Beach County.

passed

10 Southern Florida. Center passed
through northwestern corner of Palm
Beach County.
14 Extreme south. Hurricane winds at
Miami.
8 Southeast coast. Center entered east
coast south of Miami.
13 Most of Florida. 12 or more killed.
Center entered coast near Stuart.
8 South and northwest Florida. 14
killed, heavy shipping losses. Center
entered coast near Palm Beach.
15 Extreme south. Center passed through
Palm Beach County and crossed the
Coast near Stuart.




Table 3. Continued

Storm Date

Direction

Direction

Forward Speed

Principal Places in Florida Affected and Remarks

Oct. 19, 1906Sept. 18, 1926* Aug. 7, 1928* Sept. 16, 1928* July 30, 1933* Sept. 4, 1933* Nov. 4, 1935* Oct. 6, 1941*

220 110
140 120 100
120 060 110

250 100
170 150 130 150 060 080

10 A major hurricane. Southeast coast. 164
lives lost.
11 A major hurricane. Miami and northwest
Florida. About 500 lives lost; damage,
$100,000,000.
8 East coast, north of Palm Beach. 2 lives lost; damage $235,000.
12 A major hurricane. Entire peninsula.
Center passed over Lake Okeechobee area. 1826 killed; damage, $25,000,000.
7 Central Florida. Damage light. Center entered coast near Fort Pierce.
11 A major hurricane. Peninsula. Center
entered coast over Jupiter Inlet.
9 Extreme south. Center passed over Miami. 19 killed; damage, $5,500,000.
17 A major hurricane. Winds of 123 miles
per hour reported at Dinner Key. 5
killed; damage, $675,000.

BONN.-




Table 5.3: Continued

Storm Date

Direction

Direction

Forward Principal Places in Florida Affected Speed and Remarks

Sept. 15, 1945* Sept. 17, 1947* Oct. 12, 1947 Sept. 22, 1948 Oct. 5, 1948 Aug. 27, 1949* Oct. 18, 1950*

130 080 230 230 230 130 150

100 080 230 260
200 130 150

13 A major hurricane. Extreme south.
Center entered coast south-of Miami.__4
killed; damage, $60,000,000.
10 A major hurricane. Fort Lauderdale to
Fort Myers. Hurricane winds reported
along a 240-mile stretch of coast. 17
killed; damage, $31,000,000.
12 South Florida. Wind damage in Florida,
$75,000. Heavy to excessive rains.
15 A major hurricane. Southern Florida.
Center passed through Palm Beach County. 3 killed; damage, $12,000,000.
13 Extreme south. Center moved over
Florida Keys, passed close to Miami
Beach and remained off shore.
14 A major hurricane. South Florida.
Center entered coast near Palm Beach. 2
lives lost; damage, $45,000,000.
11 A major hurricane. East Florida coast.
Center passed through Miami and Palm Beach County. 3 killed; damage,
$27,750,000.




Table 5.3: Continued

Storm Date

Direction Direction

Forward Principal Places in Florida Affected Speed and Remarks

Aug. 27, 1964* Oct. 14, 1964

160
220

160 250

11 A major hurricane. East Florida coast.
Center --entered- coast- near --Miami- and passed through Palm Beach County. No storm fatalities; damage, $125,000,000.
20 South Florida. Center Passed through
Palm Beach County. 3 lives lost;
damage, $900,000.

*Landfalling hurricane from Atlantic Ocean
**Direction of hurricane movement at the time it crossed the coast:
(a) clockwise from North.
(b) clockwise from coastline.




Table 5.4: Frequency of storm levels: Palm Beach County (Ref: 7)

Return Period
(Years)

500 200 100 50
20 10

Estimated Storm Surge Level (Feet)
Northern Boundary Southern Boundary

10.2
8.8 7.7 6.5
4.9 3.9

10.0 8.7 7.5 6.3 4.7 3.7

elevation at Jupiter Inlet for the Intermediate Regional Tidal Flood and for the Standard Project Tidal Flood as 7.0 to 8.0 feet and 8.5 to 9.5 feet, respectively (Ref: 2).
The return period for various storm surge levels was estimated by the University of Florida for the coastal region of north Palm Beach County (Ref: 9). The results are given in Table 5.5.
5.4 Conclusion
Taking into account the estimated storm surge levels for Martin County and for Palm Beach County, the following values may consideredlto be relevant to studies related to Jupiter Inlet.

!Return Period
(Years)
500 200 100 50
20 10

Storm Surge Level
(Feet) 11.0
9.0 8.0 7.0 6.0 4.0




Table 5.5': Estimated return period for storm surge levels for
north Palm Beach County (Ref: 9)
Return Period Height Above M.S.L.
(Years) (Feet)
6 7 4.1 or higher
12 14 4.9 or higher
20 22 6.6 or higher
34 36 8.2 or higher
58 60 9.8 or higher
100 11.5 or higher




Fig. 5.1 Location map.




z
S14 a)
F- 12 cc North Profile /""'
0 hMiddle Profile
0
F
D Middle Profile
'10 1 05 0 0 0
z
0
L)
0 10 20 50 100 200 500
RETURN PERIOD (Years)

Fig. 5.2 Combined total storm tide frequencies for Martin County (Ref: 5).




II I I 11111 I I

Northern Boundary 4 '$
Southern Boundary

I I I I 111111

I I I I

50 100
RETURN PERIOD (Years)

Fig. 5. 3

Estimated frequency of storm surge levels for Martin County (Ref: 6).

500

I I I I I I I I I I I I I I

I I I I

I I

11111 1 1




Fig. 5.4' Hurricane tracks passing through Palm Beach County,
Florida, and vicinity during the period 1871-1970.
73




I I I I 11111 I I I I I

Northern Bo

I I I I I

undary /
Southern Boundary 11 ll I I I I

10 50 100 500
RETURN PERIOD (Years)

Fig. 5.5 Storm surge frequency curve for Palm Beach County
(Ref: 7).
74

I 1 1 i

I I

I l l I | 1 I 1




VI. SAND TRANSFER CONSIDERATIONS

6.1 Introduction
Jupiter Inlet is known to have been in existence for over 300 years, however, it has been extensively used by the local population only for the past 100 years or so for recreation and fishing. In 1892, St. Lucie inlet was constructed by making an artificial cut through the barrier strip, about 6 miles north of
Jupiter. This operation is believed to have seriously affected the regime of Jupiter Inlet. Between the years 1913 and 1922, the inlet moved approximately 1250 feet northward. In order to stabilize the
location of, inlet, two jetties were constructed at the inlet mouth. Each jetty was 400 feet in length and 400 feet apart from each other. A channel, 6 feet deep, was dredged to meet the ocean. This anthropogenic interference caused the disruption of the littoral drift in the area. Sediment deposition continues to occur within the dredged channel, inside the inlet and over the ebb shoal area.
Since the total bypassing of sediment is not achieved, considerable beach erosion has taken place on the downdrift side. Attempts have
been made in the past f rom time to time to nourish the eroding beach by transferring sand dredged from the inlet. However, these efforts have not been wholly satisfactory.
As a part of the present study, it is necessary to examine the issue of the transfer of sand to the south beach in order to limit the beach erosion. This report reviews the various alternative options of sand transfer system available at present and examines their suitability for implementation at Jupiter Inlet. A study of littoral drift and sediment budget in the area have been given. A
review of conventional systems and new technology for sand transfer has been included. Finally, after discussing the design parameters, a -sand transfer system which appears to be a technically viable option for the conditions prevailing at Jupiter Inlet has been recommended.




6.2 Site Conditions
The prominent physical features at Jupiter Inlet consist of
two rubble mound jetties at the entrance, a dredged navigation channel and a sand trap located inside the inlet (Fig. 6.1). Considerable amount of sediment deposits in the sand trap while a small amoun t is deposited in other areas of the inlet.
On the beach, the mean particle size of dunes is 0.34 mm, reducing gr adually to 0.17 mm in water depth of 20 feet. The mean diameter of sediment in the sand trap is 0.80 mm. The reason for
the coarser material in the sand trap could be that the finer sediment remains in suspension under the strong flood and ebb tidal currents at the inlet and gets carried away over the sand trap without depositing.
The me an tidal range at Jupiter Inlet is about 2.5 feet. The maximum strength of flood current is on the order of 5.3 feet per second whereas the strength of ebb current is 4.5 feet per second for a spring tidal range of 3.4 feet.
Drogue observations conducted by the University of Florida in
1990 showed that the strength of offshore current, roughly parallel to the shore, is on'the order of 1.0 to 1.5 feet per second. The offshore cu rrent is independent of the flood and ebb phase of tide; however, it has a seasonal variability as it represents the combined effects of ocean currents, tidal range and wave induced current.
The average wave height varies from 0.5 feet to 2.5 feet and the wave pe Iriod from 4.5 seconds to 10 seconds. The monthly maximum
wave heights and periods vary from 4 to 7 feet and 9 to 12 seconds, respectively.
Other'natural conditions at the site such as wind, salinity,
rainfall etc. are not relevant for the purpose of the present report. Hence details on these are not considered here. However, data on the same are presented in the First Progress Report (Mehta et al.) 1990a).




6.3 Proposed Development
The two jetties have helped stabilize the inlet against shifting it i s location, and the sand trap functions reasonably well
I
with periodic dredging. The major problem consists of continued erosion of 'the beach on the south side of the inlet in spite of transfer of sediment from the sand trap over the past 38 years. The net direction of littoral drift at Jupiter is southward and the erosion of south beach is believed to be caused by insufficient transfer of, sand across the inlet. The second problem is related to the navigation channel. The tidal velocity through the inlet is high enough to keep natural depth exceeding 10 feet. However, the outer navigation channel has not been well marked by conventional navigational aids covering the area between the inlet and the 10
foot contour in the sea. The lack of navigational aids coupled with the severe'tidal currents and waves at the inlet, make navigation somewhat hazardous for small motor launches.
The following developments are proposed at Jupiter Inlet:
1. Providing a well-defined, dredged navigation channel with 10
feet depth. Two possible alternatives under consideration are
shown in Fig. 6.3.
2. Providing a sand transfer system which could be operated on an
as needed basis so as to maintain adequate supply of sand to the south beach and thus minimize beach erosion as far as possible.
In addition to the above, dredging of a part of the offshore bar as borrow area and using the material for a beach nourishment project along the beach south of the inlet in order to widen the beach has b I een proposed. The proposed borrow area is shown in Fig. 6.3. Various considerations related to the second item are described in the following pages.
6.4 Littoral Drift
6.4.1 Previous Estimates
The quantity and the rate of movement of littoral drift along Jupiter Island has not been determined directly. However, various estimates which have been made in the past from time to time are given in Table 6.1 (DeWall and Richter, 1978):




Table 6.1 Estimates of annual littoral drift at Jupiter Inlet
'Agency New Drift Cu.Yd/Year
Quantity Direction
1. U.S. Corps of Engineers 230,000 South
i
2. DeWall and Richter
a) Das 536,200 South
b) S.P.M. 673,600 South
3. University of Florida 250,000 South
4. Bruun (1990) 225,000 South
5. Aubrey and Dekimpe (1988) 200,000 South
For purposes of this present report, it is estimated that the net littoral drift at Jupiter Inlet is southwards with an average
rate of 230,000 cubic yards per year. This is based on the analysis of dredging data and wave data as described in the subsequent sections.
6.4.2 Dredging Data Analysis
Dredging has been carried out in two areas inside Jupiter Inlet:
i) Dredging in the sand trap
The sand trap is located about a quarter of a mile west of the inlet (Fig. 6.2). Dredging is done by the Jupiter Inlet District through contractors as and when necessary, usually at intervals of 2 years. The dredged material is
transferred to the south beach.
ii) Dredging in the Intracoastal Waterway
This dredging has been carried out mainly at two locations which are shown in Fig. 6.4. The material dredged from the sand trap located at the confluence of northern and north-western arms of the Loxahatchee River is transferred to the southern beach. Sediment dredged 78

I I




from a small area inside the northern arm is transferred
to the beach north of Jupiter Inlet (Fig. 6.4). This dredging is carried out periodically by the U.S. Army C orps of Engineers. Since this is an independent
operation, it does not necessarily coincide with the
dredging of the main sand trap.
Data on the dredging quantities in both the areas are given in Table 6.2. The average quantity of sand dredged from the Intracoastal Waterway by the U.S. Army Corps of Engineers during
the years 1963 through 1988 works out to 41,180 cubic yards per year. Data on the amount of sand transferred to the south beach out of this total dredging are not available. However, it is believed that more material has been placed on the north beach than on the
south beach. Assuming that about one third of the material was placed on the south beach on the average, the estimated quantity
would be of the order of 13, 000 cubic yards per year. This estimate is later us ed for working out the sand budget under Section 6.5 of this report.
Data on the placement of dredged material on the shoreline south of Jupiter Inlet are given in Table 6.3 (Continental Shelf
Associates,' 1989a) The quantities given in the table cover a period of 37 years from 1952 to 1988. Although the sediment was transferred from two areas, namely, the main sand trap and the sand trap of Intracoastal Waterway, data on the breakup of quantities
are not available. From the data presented in Table 6.3, the average amo iunt of sediment transferred to the south beach works out to 43,513 cubic yards per year.
6.4.3 University of Florida Study
6.4.3.1 General
The University of Florida used the following data for estimating wave energy at Jupiter:
1. U.S. Naval Weather Service Command Summary of Synoptic
Meteorological Observations (SSMO); use of existing ship wave
data in the Atlantic.




Table 6.2: J.I.D. and Army Corps dredging records for Jupiter
Inlet (Dixon, Dixon and Assoc. Engr., Inc., 1991)

J. I. D.
Cu. Yd.
(Continental Shelf Assoc. Inc., 1989)

Army Corps Cu. Yd.
(Seymour and Castel, 1985)

72,075

Vol. Unknown
421000

45,100 45,000 123,000
243,000

6/52 1956 9/58 9/60 1961 8/62 1963
1964 1965 6/66 1967 6/68 1969 8/70 9/72 5/75 5/77 1979 11/81 1983 1985 1986 1987 1988

65,500 69,300

Vol. Unknown
46,000 21,800
24,000
31,500 28,000 50,000 93,500
45,000 154,000
118,800 110,500 130,300

130,300 87,000

Total Cu. Yd

Proj ect Year

131,000
77,000 76,500 102,600 93,995
93,000 75,000
60,000 76,000

72,075
42,000 45,100
45,000 46,000 144,800 24,000 243,000 31,500 159,000 50,000 170,500 121,500 256,600 93,995 211,800 75,000 170,500 76,000 130,300 195,800 156,300




Table 6.3: History of Jupiter Inlet and Intracoastal Waterway i dredging and placement of disposal material on the
shoreline south of Jupiter Inlet (Continental Shelf
Assoc., 1991)
Year Volume
(Cu. yds)
1952 30,000
1954 60,000
1956 70,000
1958 42,000
1960 45,000
1962 56,000
1964 126,000
1966 209,000
1968 120,000
1970 45,000
1972 78,000
1974 50,000
1975 85,000
1977 102,000
1983 172,000
1985 80,000
1987 65,000
1988 175,000
TOTAL 1,610,000
2. Wave hindcast using wind data at West Palm Beach Airport.
3. U.S. Army Corps of Engineers' Wave Information Study (WIS):
Hindcast model.
Data were obtained over a 20 year period from 1956 to 1975. Average monthly distributions of wave heights and wave directions were determined and wave energy calculations made. The relationship between wave energy and rate of littoral transport suggested in the
Shore Protection Manual was used to determine the rate of longshore drift.
6.4.3.2 Estimated Annual Drift
The estimated annual longshore transport for the years 1956 through 1975 is shown in Table 6.4. The table gives the quantity of




southward and northward drift separately, along with the net drift. It may be noted that the net drift was southward during this entire 20-year period. Quantity of net drift worked out for the year 1975
appears to be far too lower than those for the other years. This is believed to be due to insufficient or erroneous wave data. The average net drift for all the 20 years is 230,778 cubic yards per year, which is close to 230,000 cubic yards per year. In fact this is the rate used in calibrating the Shore Protection Manual
relationship between wave conditions and the rate of littoral drift. Therefore the value 230,778 cubic yards per year is not an
independent estimate of the net annual mean rate of littoral drift. Percentages of the quantity of southward drift and northward drift with respect to the gross drift are also given in Table 6.4. It is seen that 17 percent of the gross drift is northward whereas 83 percent is southward. The data given in Table 6.4 are plotted in Fig. 6.5. A log normal probability plot of annual longshore transport 'magnitudes (northward and southward) is shown in
Fig. 6.6.
The percentages of duration of occurrence of drift in the southward and northward directions are shown in Table 6.5 for each year over the period 1956 to 1975. The data are plotted in
Fig. 6.7. It is noted from Fig. 6.7 and Fig. 6.6, respectively, that while, the average duration of occurrence of drift in the southward and northward directions are 60.7 and 34.8 percent, the
corresponding sediment volume rates are 82.9 and 17.1 percent. This indicates that the wave climate inducing northward drift is considerably milder than that producing southward drift.
6.4.3.3 Estimated Monthly Drift
Quantities of monthly littoral drift were estimated using the same procedure as described in the previous section. The results of calculations made for a single year, 1967, are given in Table 6.6 as an illustration and the same are plotted in Fig. 6.8. It is
noted that during the four month period May through August, the net drift was northward and in the other eight months it was southward,
82




Table 6.4:

Estimated longshore transport values (Q cubic yards/year) for 20 year period 1956-1975 (calculated from WIS wave hindcast data)

Qsouth
Cubic Yards Per Year

433,633 207,214 381,848 310,889 236,324 147,716 261,973 232,033 146,029 225,910 255,891 270,685 63,430 194,132 203,480 190,001 316,316 316,063 200,821 21,181
251,720

473,253 278,450 441,072 395,503 302,862 228,766 321,219 286,333 210,080 291,087 346,656 315,307 98,922 253,204 273,624 246,245 375,529 382,845 227,965 78,744

North

-39,621
-71,236
-59,223
-84,614
-66,538
-81,050
-59,245
-54,299
-72,050
-65,177
-90,766
-44,622
-35,492
-59,072
-70,143
-56,244
-59,214
-66,781
-27,144
-57,563

Qsouth
+Qnorth

512,874 349,686 500,295 480,117 369,400 309,816 380,464 340,632 282,130 356,264 437,422 359,929 134,414 312,276 343,767 302,489 434,743 449,626 255,109 136,307

Percentage of Gross Drift
% South % North

92.3 79.6 88.2 82.4 82.0
73.8 84.4 84.0 74.5
81.7 79.2 87.6 73.6
81.1 79.6
81.4 86.4 85.1 89.4 57.8
82.9

7.7
20.4 11.8 17.6 18.0
26.2 15.6 16.0
25.5 18.3
20.8 12.4
26.4 18.9
20.4 18.6
13.6 14.9 10.6 42.2
17.1

*These data are excluded from analysis because they do not appear reliable.

Year

Qnet

1956 1957 1958 1959 1960 1961
1962 1963 1964 1965 1966 1967 1968* 1969 1970 1971 1972 1973 1974 1975*
Average




Table 6.5: Estimated percentage of duration of occurrence of
southward and northward drift for 20 year period
1956-1975 (calculated from WIS wave hindcast data)
Percentage Duration of occurrence Year %Southward %Northward %Zero
1956 67.3 28.2 4.5
1957 72.2 27.6 0.3
1958 61.4 31.4 7.2
1959 60.7 36.8 2.4
1960 55.2 42.4 2.4
1961 53.8 42.2 3.9
1962 58.5 34.0 7.5
1963 56.4 33.7 9.9
1964 55.2 41.0 3.8
1965 56.9 39.1 4.0
1966 64.3 34.6 1.0
1967 64.2 32.6 3.2
1968 53.9 39.7 6.4
1969 56.5 36.1 7.4
1970 67.5 32.1 0.4
1971 52.8 38.8 8.4
1972 74.1 25.5 0.4
1973 66.0 33.5 0.5
1974 49.3 36.7 14.0
1975 31.5 50.4 18.0
Average 60.7 34.8 4.5




Table 6.6:

Estimated net monthly littoral drift for the year 1967

Month

Southward

Cubic Yards/Month
Northward

January' February March April May
June July
August September October, November December

Total for the year

28,600 39,760
34,420 13,090

2, 100 5,660 7,110 3,390

16,800 48,810 77,400 29,900
288,780

Net Southward for the year: 270,520 cu.yd. Southward and Northward for the year: 307,040 cu.yd.

18,260




of which 44 percent occurred during two months, October and November.
Monthly drift was calculated for each of the twenty years and the average of twenty year data for each month was determined. The magnitudes of mean southward, mean northward and gross drift are
given in Table 6.7 along with the percentages of volume with respect to gross drift.
Monthly magnitudes of net southward and net northward drift
are given in Table 6.8 based on the 20 year calculations along with the corresponding percentages with respect to the total drift (southward plus northward) The monthly percentages are plotted in Fig. 6.9.
The following conclusions are drawn from the above analysis of data:
1. Northward drift takes place mainly during a two-month period
of June and July. The quantity of drift being 2.4 percent of
the gross drift.
2. Both southward and northward drifts take place during each
month.' During the four month period October to January, the average southward drift is 80 percent and northward drift is 20 percent of the total volume of gross drift. Hence there is
a net southward drift. During June and July the average southward drift is 34 percent and northward drift is 46 percent of the total volume of gross drift. Hence there is a
net northward drift.
6.4.3.4 Estimated Daily Drift
Results of computations of daily littoral drift are shown in Fig. 6.10 for the year 1967. This figure gives the cumulative net southward longshore littoral sand transport for the Jupiter area. Since the net drift during the year 1967 was northward during May
through August, Fig. 6. 10 indicates a decrease in the net southward transport over this period. It may be noted that during the month of November, there is a sharp increase in the cumulative southward
transport. It has been estimated that during the two-day period of




Table 6.7: Estimated monthly magnitudes of
WIS wave data

littoral drift, based on 20 years (1956-1975)

Mean Mean

Mean
Southward cu.yd/yr

Mean
Northward cu.yd/yr

Southward
and
Northward cu.yd/yr

% Volume Southward

% Volume Northward

January February March April May June July August September October November December Total

Qnet = 246,347 cu.yds/yr

Month

55,016 40,870 36,300 23,562 13,957 7,600 1,935 5,450 29,820 62,956 66,616 58,120 402,202

11,256 19,326 18,035 18,410 10,820 9,430 6,258 4,826 9,875 15,213 13,440 18,966 155,855

66,272 60,196 54,335 41,972 24,777 17,030 8,193 10,276 39,695 78,169 80,056 77,086

83.0 67.9 66.8
56.1 56.3 44.6 23.6 53.0
75.1 80.5 83.2
75.4

17.0 32.1 33.2 43.9
43.7 55.4
76.4 47.0 24.9 19.5
16.8 24.6




Table 6.8: Estimated monthly magnitudes of net southward and
northward littoral drift based on 20 years (1956-1975)
WIS wave data

Net
Southward cu.yd/yr

Net
Northward cu.yd/yr

% of Gross Drift Southward and Northward

January February March April May June July August September October November December Total

Net Southward = 246,347 cubic Total Southward and Northward

yards
= 258,653 cubic yards

Month

43,760 21,544 18,265 5,152 3,137
624
19,945 47,743 53,176 39,154 252,500
(97.6%)

1,830
4,323

16.92 8.33 7.06 2.00 1.21 0.71 1.67 0.24
7.71 18.45 20.56 15.14 100.00

6,153
(2.4%)

L




7th to 9th November 1967, the net southward transport was 15,840 cubic yards per day, or a total of 31,680 cubic yards during the two days. Since the total northward plus southward sediment transport during this year was 307,040 cubic yards, the two-day volume is equivalent to 10.32 percent of the gross annual sand transport. The average daily transport rate of the gross drift (southward plus northward) over the one year period works out to 841 cubic yards per day. The peak transport rate over the two day period works out to 18.83 times the average daily rate. The occurrence of such high rates of transport over a relatively very short time span is not at all uncommon. In fact, similar
observations have been made at other locations along the U.S. coastline a nd also at other places in the world. Seymour and. Castel (1985) have reported that nearly 50 percent of longshore drift occurs during 10 percent of the time associated with storms. Studies related to estimation of beach erosion and effective sand
transfer need to take into account such episodic occurrences of high transport rates.
6.4.4 Characteristics of Littoral Drift at Jupiter
The important characteristics of littoral drift at Jupiter may be summarized as follows:
1. Littoral drift estimates based on WIS wave data over a 20 year
period from 1956 to 1975 indicate that southward drift occurs
for a total of 60.7 percent of time and northward drift occurs for 34.8 percent of time during a year on an average basis.
There is no drift during 4.5 percent of the time, either because there is no significant wave activity or because the
waves are normal to the shore.
2. The wave climate that induces northward drift is milder than
the wave climate that induces southward drift. The total volume of southward drift is 82.9 percent of the gross volume wherea s the northward drift accounts for 17.1 percent. The volumetric percentages are not proportional to the percentages
of duration of occurrence.




3. The net average drift for 20 year period (1956 to 1975) is
230,000 cubic yards. The estimated net minimum drift is 146,000 cubic yards per year whereas the maximum is 434,000
cubic yards per year.
4. It is !estimated that under the present site conditions, about
73 percent of the net southward drift bypasses the inlet through natural processes, 26 percent enters the inlet and 1
percent is deposited on the outer shoal.
5. The peak daily transport rate can be as high as 20 times the
average daily rate.
6. Field studies conducted by the University of Florida show that
some of the sediment from south beach is transported around the tip of the south jetty and enters the inlet. The quantity
of such transfer is estimated to be on the order of 10, 000
cubic i yards per year.
7.8. Due to variability in the wave climate at Jupiter,
considerable variability prevails in the monthly quantity and direction of littoral drift during a year and also from year
to year.
6.5 Sediment Budget
6.5.1 General
A sediment budget is based on sediment erosion, transportation and deposition, and the resulting excesses or deficiencies of material quantities. Usually, the sediment quantities are listed according to the sources, sinks and processes causing the additions and subtractions. For purposes of the present study, the net littoral drift in the study area is taken to be predominantly southward with the rate of transport being 230,000 cubic yards per year. The distribution of this quantity over different areas has been estimated.
i
6.5.2 Primary Distribution
The p 1 primary distribution of net southward drift may be considered to be as follows:




i) Sediment transferred southward naturally:
It was concluded from the beach erosion study conducted by the U.S. Army Corps of Engineers (1966) that about 73 percent of
the net littoral drift bypasses the inlet through natural processes. Hence this quantity is estimated to be 168, 000
cubic yards per year.
ii) Sediment entering Jupiter Inlet:
Most of the sediment entering the inlet probably moves in and out with the flood and ebb currents which are fairly strong.
However, the amount of sediment flushing out of the inlet during ebb is smaller than the total sediment entering during flood It is estimated that the residual sediment deposited inside the inlet is of the order of 60, 000 cubic yards per year.'It has been pointed out in Section 6.4.2 that over the past 37 years, sediment dredged from areas inside the inlet and deposited on the south beach has averaged to the rate of 43,500 cubic yards per year. The sediment enters the inlet at
the rate of 60, 000 cubic yards per year and the dredging accounts for 43,500 cubic yards per year. The differential sediment is mostly deposited inside the inlet in areas other than the sand traps and a small amount of sediment is washed
out of the deposited sediment during ebb flow. iii) Sediment depositing on the outer shoal:
A study of the growth of ebb shoal in terms of its size and
change in water depth indicated that the long term mean deposition rate on the shoal is of the order of 7,000 cubic
yards per year. out of this, 2, 000 cubic yards per year is believed to be depositing directly out of the sediment bypassing the inlet naturally and 5,000 cubic yards per year
depositing out of the sediment-laden ebb jet fanning over the
ebb shoal.
Hence, the estimated primary distribution of the net southward
i
drift is as follows:




j ~cu. yds. /yr 1.Transferred southward naturally: 168,000
2. Entering Jupiter Inlet: 60,000
3. Deposited on outer shoal: 2.000
Total 230,000
This primary distribution is shown in Fig. 6.11.
6.5.3 Secondary Distribution and Return Flows
The secondary distribution consists of the fate of sediment
entering Jupiter Inlet and this may be considered to be as follows: i) Sediment depositing in the sand traps:
Dredging records shown in Table 6.3 show that sediment is dredged at an average rate of about 43,000 cubic yards per year. In the absence of actual data, it is estimated that out of this total quantity, 30,000 cubic yards are dredged from the channel trap and 13,000 cubic yards from the Intracoastal
Waterway's trap.
ii) Sediment deposition inside the inlet:
Sedimentology of the lower Loxahatchee River Estuary and Jupiter Inlet studied at the University of Florida (Mehta et
al., 1990b) revealed that the flood tidal delta located at the intersection of the Southwest, Northwest and North Forks of the Loxahatchee River is extending itself into the mouth of
Northwest Fork, causing shoaling of the boat channel. Although it is not absolutely clear where the sediment is coming from, both the longshore transport system and the fluvial transport system may be making significant contribution. Bank erosion also contributes to the shoaling process. These conclusions are based on the similarity of textural parameters in
different deposits. It is thus evident that a part of the sediment entering Jupiter Inlet is lost from circulation due
to deposition in the inner areas of inlet. It is estimated that the average annual quantity of this loss is of the order
of 7,0 !00 cubic yards.




iii) Other factors:
A part of the sediment from the inlet is flushed out during ebb flow. A fraction of this sediment is deposited over the ebb shoal when the sediment-laden ebb flow spreads over a large area outside the inlet. The sediment which does not deposit over the shoal is flushed out in the net southward direction under the combined action of tidal currents, ocean
currents and wave-induced currents.
Thus, out of 60,000 cubic yards entering the inlet, the estimated distribution is as follows:

1. Deposited in channel sand trap:
2. Deposited in Intracoastal Waterway and
other inside areas:
3. Sediment flushed out of the inlet during
ebb flow:

cu.yds/year
30,000 20,000 10,000
Total 60,000

The above secondary distribution is shown in Fig. 6.12. The return flows consist of the following: cu.yds/year

1. Sand dredged from the channel trap and
transferred to south beach:
2. Sand dredged from the Intracoastal
Waterway trap and transferred to south beach:
3. Sediment flushed out of inlet and
a) deposited on the ebb shoal:
b) flushed out southwards:
4. Scattered deposits inside the inlet:

30,000
13,000
5,000 5,000 7,000
Total 60,000

The return flows are shown in Fig. 6.13.




Net Annual Southward Drift: 230,000

6.5.4 Total Distribution
Taking into account the primary distribution, the secondary distribution and the return flows of sediment, the estimated quantities of total distribution are shown in Fig. 6.14. The same
distribution in the f orm of percentages with respect to the net annual southward drift is given in Fig. 6.15.
The distribution chart is as follows with quantities given in cubic yards:

Lost in Transit: 14,000 (6%)
Outer Shoal: 7,000 (3%)
Inside Inlet: 7,000 (3%)

Transferred Southward: 216,900
(94%)
Entering Inlet: 60,000 Natu

rally ; Transferred

Deposit on Outer Shoal:
2,000 (1%)

(26%)

Southward: 168,000

(73%)

Deposit in Channel Sand Trap: Deposit in Intracoastal Waterway: Scattered Deposits Inside Inlet: Ebb Flow Deposit on Outer Shoal: Ebb Flow Sediment Flushed Southward:

30,000 (13.0%) 13,000 (5.6%) 7,000 (3.0%) 5,000 (2.2%) 5,000 (2.2%)

6.5.5 Sources of Southward Sand Transfer
The net southward sand transfer at Jupiter Inlet occurs due to natural bypassing as well as due to human efforts consisting of dredging inside the inlet and placing the sediment on the south
i I
beach. The distribution appears to be as follows:
94




Cubic Yards/Year
Natural bypassing in deep water 168,000
Sediment flushed out of inlet 5,000
Sub-total 173,000
Dredging and deposition 43,000
Total 216,000
Thus, out of the estimated 230,000 cubic yards per year, about 14,000 cubic yards per year are not transferred to the south beach. This sediment is "lost" in the form of deposition on the outer shoal and deposition in different areas inside the inlet. This deficit of sediment as well as the deflection of the littoral drift by the inlet jetties is believed to be causing erosion of southern beach and hence the quantity of sediment transferred through human efforts needs to be increased at least by the order of 14,000 cubic yards per year.
6.6 History of Beach Nourishment at Jupiter
Beach nourishment projects have been completed from time to time on Jupiter Island beach north of Jupiter Inlet. Offshore borrow areas generally used for dredging are shown in Fig. 6.16. Aubrey and DeKimpe (1988) have examined in detail the performance of beach nourishment carried out at Jupiter Island beach. Locations
of the nourishment areas during four projects from 1973 to 1987 are shown in Fig. 6.17.
The following measures against beach erosion have been taken to protect the 8 km long beach of the town of Jupiter Island:
1. Four major beach nourishment projects (see Table 6.9)
contributing more than 8 million cubic yards of sediment at a
cost of $11.5 million.
2. Several smaller nourishment projects contributing an
additional 1 million cubic yards of sediment.
3. Construction of nearly 8 km of seawalls and revetments
combined with more than 5 km of coast protected by groins.




Table 6.9:

Beach 1988)

nourishment projects at Jupiter Island, Florida (Aubrey and DeKimpe,

Volume Nourished (*106c.y.)

Dredging Cost
$/c.y.

Nourished Length
(ft)

Continuous/ Segmented

continuous continuous
segments: 2,588'N
3,600'S continuous
segments: 5,850'N
3,150'S
segments: 3,125'N
10,833'N 3,542'S

N = north beach fill, M = middle beach fill, S = south beach fill

Project

Year

1973 2.52 1.00 16,800

1973
1974 1977 1978 1983
1987

2.52
0.97 0.48
0.85 1.00 2.23

1.00 1.00
1.28
1.28
2.40
1.63

16,800
9,200 6,188 7,650 9,000 17,500




The history of shoreline maintenance/ construction is given in Table 6.10. A comparison of pre-nourished and post-nourished mean grain size on the beach is given in Table 6.11.
After reviewing the performance of beach nourishment at Jupiter Isl and, the following conclusions were drawn by Aubrey and DeKimpe (1988):
1. The ongoing beach nourishment project has been successful at
Jupiter Island, if success is indicated by the protection of houses and property from storm damage, and by the net
accretion of sediment on the beach.
2. While the annual net longshore sand transport rates for this
region of the coast are estimated to be approximately 200,000 cubic yards, net addition of sediment to the beach through renourishment has averaged 320,000 cubic yards per year over the interval 1957 to 1988, and up to 370,000 cubic yards per year from 1972 to 1988. This excess loss of material from the project area reflects in large part of the high fine content
of the borrow material.
3. While theory suggests that use of coarser sand on Jupiter
Island beaches would decrease renourishment requirements by
about a factor of 2 to 4, the basis for making these estimates is largely empirical and fraught with uncertainty. It is not clear that a sponsor is going to pay significant additional costs for this coarser material, given the level of uncertainty (and hence risk) in these engineering
calculations. This situation points to a clear need for improved understanding of beach response of varying grain sizes to different wave conditions, and for improved monitoring of existing beach nourishment projects to improve
our empirical basis for predicting response of beaches of different grain sizes to wave attack. Existing methods are grossly inadequate for detailed cost comparisons at Jupiter
Island.
4. Improved dredging technology and upgrading of dredging
equipment might lead to reduced costs for long-distance




Table 6.10: History of shoreline maintenance/construction at
1 Jupiter Island, Florida (Aubrey and DiKempe, 1988)

Year

Proj ect

1945-1955 1957-1958 1960-1961 1961-1962 1964-1968 1966
1970-1972 1973-1974 1983
1987

Table 6.11:

Construction of 8,000 linear feet of sheetpile seawall.
Nourishment with 254,000 c.y. from ICWW. Nourishment with 366,000 c.y. from ICWW. Construction of 7,760 linear feet of sloping revetment wall.
Nourishment with 363,000 c.y. scraped from offshore.
Construction of groins every 100 feet with 3 miles.
Nourishment with 280,000 c.y. from ICWW. Nourishment with 3,500,000 c.y. from offshore pits.
Nourishment with 1,000,000 c.y. from offshore pits.
Nourishment with 2,230,000 c.y. from offshore pits.

Grain size comparisons at Jupiter Island, Florida (Aubrey and DeKimpe, 1988)

Pre-nourished Beach

0.29 mm
0.76 mm (shoreline)

0.24 mm 0.27 mm*

Dredge Material

0.12 mm 0.12 mm 0.15 mm*

Post-nourished Beach

0.35 mm
0.42 mm 0.27 mm* 0.19 mm*

*Indicates mean grain size (otherwise median grain size)

Year

1968
1973 1974 1977 1978 1987